Oh and another couple things I forgot to add. Should I be lubing my O-rings after every dive? and I'm really scared that my housing will leak for some reason.. and when Inspecting the O-ring on my WP-38 I can see tiny little specks of dust or particles, is that anything to worry about? P.S. I still have not used it, Ive only taken it out of the box so far and tested everything out.
You always want to have a lubed and clean O-ring.
A good rule of thumb is that if you open the camera, you (at least) inspect the O-ring (for cleanliness).
Similarly, another good rule of thumb is to tell yourself that you won't open the camera more than
X times without pulling out the O-ring to clean & relube it. My personal rule of thumb is
X=2
Finally, you'll also want to open up the housing after
Y number of dives and clean & relube it anyway. My personal rule of thumb here is absolutely no more than
Y=4 for the main housing rings, aalthough I will sometimes slide on some of the smaller (and known-robust design) Ikelite Synch Cord O-rings a little longer. Follow at your own risk, and remember that familiarity breeds contempt (and flooded photo gear).
It would be a good idea that when you get to deep water with it for the first time, leave the camera on the boat and take the housing down to depth and run through all the controls multiple times just to make sure the housing is good. Occasional manufacturing defects do occur with the Canon housings.
True, although its a bit smarter to go do this wet test ASAP in the local dive shop's swimming pool.
The 8-10 feet of water in a pool is plenty if there's a leak problem, and doing this sooner gives the new equipment owner a chance to get any found-bad equipment replaced before he goes on his expensive dive trip. Bring along the camera too, so that you can then do a quick test snorkel in the pool with the camera in the housing too, to check out the controls ... and also your dive mask (see next).
I would make sure I can change ALL settings on the housed camera blindfolded------no peaky peaky....
From 20 years with a Nikonos, I did get to this level of "blindfolded" but I hadn't noticed that my perscription dive mask had gotten woefully out of date until I moved to a new UW camera system and suddenly realized that I could no longer read any of the settings. As such, it is also important to check out that you can actually read the camera/housing controls while underwater with your regular dive mask on. Spending another $200 or so for a new perscription mask is cheap in comparison to the cost of an UW camera system.
What is the best way to clean your O-Ring?
The basics are that you want a lint-free material of some sort. Since you'll also be getting some O-ring grease on it, it is helpful if it is easily washable in the laundry.
The recommendation I received when I received my UW camera training two decades ago was "Borrow an old towel from a cheap hotel that's nearly dead because it has been through the wash a million times". I've used many Resort "Complementary Swimming Pool" towels and I carry with my gear one small bathroom hand towel that I've been using for the past 20 years that I'll leave in my hotel room ... it is just getting broken in, so I think I could be conviced to part with it for a mere $50 ...
you were warned that UW photography was expensive, right? 
FWIW, I carry and occasionally use Q-tips to clean out various O-ring grooves, but I then have to visually inspect the cleaned groove to make sure that it didn't leave behind any fibers.
Finally, when you're putting grease back on your O-ring, the old rule of thumb for doseage of the grease is "one for you and one for the O-ring." You don't want too much and you don't want too little .. a balancing act .. and you also want to make sure that the grease you do use gets thoroughly distributed along the entire O-ring.
My personal O-ring greasing SOP is as follows. I'm right-handed, if that makes any difference:
0. Start with a clean & dry O-ring ... and clean hands. Both hands.
1. Dab my right index finger (twice) in my grease
2. Touch my greased index finger & thumb together
(this spreads it from finger to the thumb too)
3. Hold O-ring in left hand
4. Pinch the O-ring in a couple of random locations with my greased right hand finger/thumb
(this pre-positions some grease to where it will be needed, which is more important on large O-rings)
5. Grab (gently) the O-ring in a "pinch" with my greased righthand thumb/index finger.
6. Regrip the O-ring with my left hand's index/thumb to be right next to the greased right hand
7. Pull hands apart - this causes the O-ring to slide between the greased fingers, spreading out the grease.
Be careful to not pull too far (risk of stretching the O-ring) Take note of how "draggy" it feels, to note your progress
8. Regrip left (Step 6) & repeat the pull (Step 7).
9. Repeat #8 until the entire O-ring has been pulled through the greased fingers at least once (ie, the O-ring's full circumference).
On the first time going around, there should be an obvious change in how hard/easy it is to pull the O-ring when you reach the end of the dry (unlubricated) O-ring and you're overlapping back onto your previously greased O-ring section
Now here's what they don't exactly tell you in the books. It's what I call the "pull-pull-pull-rotate-pull-pull-pull" dance:
9. Twist or rotate slightly the hold on the "pinching" greased fingers on the O-ring.
10. Start pulling again (steps 6-9)
What you're doing here is a second lubrication pass that's slightly different from the first one. Note that you're not adding any more lube, but simply restributing it more thoroughly. The reason for it is because if you're really going light on grease (like they tell you to do), the pinch may have been incomplete, which can leave a dry 'streak' running around the full circumference of the O-ring, so the regrip twist/rotate is to move your fingertips relative to the O-ring's cross-section to get rid of any circumferential dry spots. There may also be some rotational wet/dry spots too, so going around a second time helps knock these out too.
11. Repeat Steps 9 & 10
If repeating once is good, repeating two or three times is better. Your hands are already greasy and all of the prep work is already done, so this literally only takes a few more seconds...like literally 5-10 seconds for 1-2 more times around the full circumference of a big O-ring.
12. "Am I done?" Check. When it is pulling smooth all the way around with no snags no matter how your greased hand is holding it, you're done. Of course, if you feel anything like "Rough Grains of Sand", you definitely have a dirty O-ring (major leak risk). Stop, find the offending contamination & eliminate it. How bad it was will determine how many steps back you have to restart.
13. "Okay, I really am done...almost": hold up the O-ring with your right (greased) hand and give it a visually inspection. What's most likely to be found here are soft stuff (hairs, etc) that aren't as obviously found by feel/touch. These can often be simply picked off by (left) hand and then the pull-pull-rotate-pull-pull repeatd to resume...figure at Step 8 or so.
14. Check it again one last time. If it really is good, then continue holding it up in your right hand. Touch your left (less greasy) hand to your (lint-free) cleaning towel to have a "dry" hand to work with for its destination on the camera gear.
15. Without ever putting it down or letting it touch anything else, install the O-ring where it goes.
16. This O-ring is done.
If you're moving to your next O-ring and you've already cleaned & prepped them ahead of time, you might not have to re-clean your greasy right hand...you now only need to do one dip into your grease.
-hh
