An altered wheelbase will affect the sensitivity of moving around on the quad. The shorter you go, the more pronounced the effect will become. Going from a +4 to +2 is not as significant as +2 to stock length, etc. It's close, but not equal.
The rule of thumb is to go as short as possible...
I'm a fan of Holeshot tires. On the other hand, tons of people like both and both have won championships in different types of riding. My recommendation is to buy whichever is cheaper for the size you're after. Fwiw, Holeshot MXR6 provide enough forward traction for most bikes up to 65hp...
With air, you will be moving too much to do any accurate work while also controlling the hand valve. The best way IMO is to find a foot controller and run the valve at the handpiece at 100%. Speed would be controlled by the valve at your feet.
Once you use foot control, you'll never look...
Grizzly doesn't sell a right angle piece to my knowledge, but their motor and shaft will mate directly to the CCS piece. That'll save a large chunk of change by not having to buy the CCS motor and straight piece.
Foredom makes a good unit, but the bulk of the components are made by the same company that makes the Grizzly and CCS stuff. As such, the parts are interchangeable.
The foredom right angle piece is a bit larger than the CCS units. I'm not really a fan of it.
Bell is a good book to learn by, but I feel that Jennings had a bit more practical info. Bell's book can be found on Amazon for a pretty decent price. There a few more books with some very arcane information, but good luck finding them in digital or analog formats. I tried for nearly 3 years...
MacDizzy was the sh*t back in the day. These days, porting is much more advanced.
His information may not be correct, but it will inform you of the considerations that need to be taken into account.
Porting is one of those things where buying the tooling to DIY will not save you money. The only time I'd recommend anyone get into porting is for the sake of learning to port. By the time you have everything needed to successfully port a cylinder without having to improvise, you can be 2/3 of...
4mil serval (421cc),
Redline race gas domes,
MX porting,
VF4 reeds,
CPI small bore inframes,
33PWK,
K&N Pods,
+6 timing,
VP110,
Built by Cam at Redline Racing