I have flown hundreds of flights on my Venture and you'll love it.
1)Individual (hatch mounted as you call them) are easy to do on the Venture. I did that with mine and I'd highly recommend it.
2)I "clipped" my Venture one bay on each wing and it flew great.
3)My guess would be no. Couldn't hurt, but you would save very little weight.
4)A 61 two stroke would do fine. I initially flew mine with an OS 70 four-stroke and it was fine. It would not do unlimited vertical. I happened to have a Saito 125 four-stroke(similar weight as the OS 91 four-stroke) and that was fun. The vibration does take a toll, however. The plane should fly fine with a 60 sized two-stroke, and no, ground clearance will not be an issue. I'll attach a pic of mine with Saito 125 and the huge prop it required.