I too would highly reccomend a BP/Wing set up.
I have no experience with that BC, but know that after using a BP/Wing for about 10dives and using another BC after I hated the other BC. Of course if you're dead set on the ScubaPro BC, buy it then, but if you can, try out a BP/Wing first just to see... and do at LEAST 4-6dives with it before saying you like it or not... Most everyone takes at least that many dives to get used to it.
The Regulator... I have no experience with the Mk16 first, but I just bought the Mk25 and the way I understand it, they breathe the same, if memory serves the Mk16's major differences from mine are non-swivel, and diaprham instead of piston (features which I had sort of wanted, over the swivel and piston, but really didn't care too much about.)
I would deffinately get the G250HP, S550, or S600 for the primary however. I have the S550 and R380 as my 2nd stages (bungeed backup as well) and though I didn't notice MUCH of a difference in breath-ability in the two second stages, I noticed enough more difficulty in the R380, that I know it wouldn't be as nice to breathe at depth of 50+ feet. Sure I only have used mine in 14' of water so far, but I've used enough regs at this point to make an educated guess on how the pool performance will compare to that at depth. I personnaly could probably live with the performance of the R380, but I'd rather have the nicer regulator... Think back to what you used in Open Water, probably VERY similar in performance, my best comparission would be the Aqualung Titan (best direct comparisson reg I've used) which works fine in the pool and shallow water, but take it past 40-50feet and you will notice the difference.
My S550, and Mk25 cost me about $403, and the R380 cost me $177 ish... Last I looked a "Safe Second" or "Air2" (whatever you want to call it) costs a little more than that, and probably doesn't perform anywhere near as well... I too have read many a threads of guys getting them, and throwing them out later... but I've seen a few people who actually use the things too (maybe they've never tested it)
Nothing wrong with the depth gauge for the most part... I bought a used Sunnto Eon Lux (air integrated Computer, with compass) a while back, before my decision to go more the DIR approach, and like it, I secure it the same way I would if it were just a brass SPG, and haven't had a problem with it. That said, if I could do it all over again, knowing what I know now, I would have bought a wrist mount computer/bottom timer (I would do the computer personally, one which could doulbe as a bottom timer if I get into DECO diving) and the SPG. It shouldn't cost much more to go that route (with wrist mount compass) than the digital gauge, if you don't go with TOP of the line computer (just a mosquito or something)
Not that I want to discourage you from your choices, or anything, but this is what happened to me when I first thought about buying gear, people encouraged me to change my choices, and I'm glad I did... I've maybe spent $200 more on the reg than my 1st choice, and $50 more on the BC, both of which I'm already MUCH happier with.
My biggest concern in your choice would be the regulator... if you buy that, you will probably end up ditching the Air2, and buying a new 2nd stage to use as a primary, very shortly, the rest of the gear, I know many people who use thoose types of configs and are VERY happy, I personnally feel however that there is a better way.
ut: )
