I will second the advise that many have given already, and hopefully expand upon it a bit. I suggest:
3mm full
- As mentioned by many, more protection from jelly and hydroid stings. The more cover the better.
- Back zip is way easier to put on/take off, especially when wet.
- I've never been too warm on 3mm full
- Add a 2mm hooded vest if you find your core feels too cold on repetitive dives.
Also add Booties, 3mm or 5mm, doesn't really matter as long as they fit well, but I suggest "high top" booties. No skin gap at the ankle, and less sand and water exchange in the booties. (I guess 5mm can provide a bit more protection from poor fitting rental fins)
Wrist and Ankle zips are nice, but not required. They certainly add convenience, but also increase the price.
Watch a few vids on YouTube on technique, but I suggest putting on your wetsuit by turning it inside out, insert your feet then Roll it up your legs, pull it up to your waist then adjust the suit on your legs and in the crotch area. (Major benefit here is reduced friction than sliding, and you shouldn't "overheat" and sweat while donning the lower half.) Then do the same process with the arms and up n over the shoulders. Not only is this method easier, but also better for the life of your suit (less stretching and pulling, thus less stress to the material).
*Major tip here: Before zipping up, if you can, step under a rinse shower or jump in the pool. This has two benefits, 1st, it is easier to finish any adjustments needed (twist the leg into place, make sure the shoulders/armpits are good.) And 2nd, the water that is now inside your suit will be preheated before you splash in, helps prevent any "Oh that's colder than I thought" shock.
**Bonus tip, IF you pee your suit during the dive (hey, we all do right?
), if you hand up your BC before climbing back onto the dive boat, unzip the back of your suit and dunk down a bit. The water will rush in and flush your suit as you climb out. Or hit the rinse showers ashore and flush out Before removing your suit.
I dive the Philippines, with water temps between 25 to 19°c. Never been "too" cold, but having a 2mm hooded vest option is nice on repetitive deeper dives during January/February, they're also inexpensive.
Happy diving and good luck to ya!