I really don't want to parrot what has been said before, so I'll throw out JUST my personal experience:
I was a college student (just graduated) with practically no income. I bought a BPW, dove around in BM for a while, and then saw sidemount. I decided I wanted to try it out, but I didn't want the cost associated with a dedicated SM rig. I mean, they're expensive! The only difference is the stupid wing tacoing, right? No big deal! I took bungees, paracord, clips, snaps, and over a hundred hours getting my rig "just right". Well, then I saw a picture of myself underwater. My tails were WAY too high, my valves were WAY too low, my wing was tacoing all over the place. It was a mess. Like, SERIOUS mess. I hated SM, I hated Tech diving, the lot of it. Then I got a chance to trade my BPW for an SMS100, so I did. Worst case, I could always trade it back in for a BPW, right? I started playing around with SM in it, and it was instantly MUCH better....but I still couldn't quite figure it out, despite dozens of dives and a so-called "experienced" SM/Tech mentor and it still wasn't right. I took my Cavern/Intro course with a TRUE sidemount instructor, and I'm MUCH better off now. My tanks are actually in-line where they're supposed to be. It's a MUCH more natural, comfortable experience. I'm MUCH happier than I thought I would've been. That training was with steels. I got a little mentorship in MX with alu tanks and I'm WAY better of with those than I was. I mean, I had a lot of help with sidemounting steels....and very little luck sidemounting aluminum tanks on my own.
I'm an Aerospace Engineer that is mechanically inclined and I love fiddling with and playing with stuff. I was working as a DMC, so I had PLENTY of time in a pool with others to help me tweak my configuration...and I had a lot of OW time trying to figure it out as well.
---------- Post added October 21st, 2013 at 02:29 PM ----------
Also, to expand on your question about the difference between slinging bottles on a BPW and true sidemount, I think a few clarifications should be made:
Tacoing is more than just aesthetically unpleasing. It can drastically reduce effectiveness of dumping air from your wing, and can make your power inflator hard to reach....also adding danger. Your wing should be flat to work as it was designed.
Slinging bottles normally puts them MUCH lower and less straight than they would be in SM. In "proper" SM, the valves go under your armpits and the body of the tank follows your body. The tanks should be FLAT while you're flat, to reduce drag. This also protects the valves and first stages, and prevents damaging the environment. BPW-slung bottles hang either far beneath you, or at awkward angles (look at most BO on CCR, they look awful).
Another need for an instructor: Proper SM procedures go into more than just how to set up your SM config and get your tanks trimmed right, it should also go into the why's and how's of your setup so you can defend it with logic. The other crucial component is the fact that many safety procedures are unique to SM. There's also a change in "how" to do certain things that only an experienced SM diver can teach.
As for instructors in your area, I don't know of any....but I have little or no experience in that area. I would try searching around regional forums. Before you pick an instructor, make sure they're properly vetted. Also, see if they have a SM rig you can borrow to see how you like it, so that you can eventually buy the one that you actually want.