1) Is there a reason to only field 5x RAS (regular assault squad) in the RB's? Why don't they go in 10s so you can have 2 Meltas or something per RB?
Because Razorbacks only have a transport capacity of 6 models. That means you can fit 5 Assault Marines and a character of some kind inside at most.
2) Some lists do a SGT with Power Fist in each RB and others go Melta and others do Flamers. What's the best way to equip these 5 man RAS units?
Different people have different ideas. Personally I prefer a Sergeant with a power weapon and one model with a meltagun. Others might prefer power fists or flamers or what have you.
3) Why upgrade the RB's with TL-something? @ 11 armor sides and front theyll pretty much get shot down really fast then
Sure, but if you're fielding 4-6 of them it's going to be nigh impossible for your opponent to take them all down before they do their damage. Also, since BA Razorbacks are fast, it's possible to move 12" and still fire a weapon which is a great advantage as you can get into range with shorter ranged weapons or maneuver into position for side armor shots.
4) With all these small squads how do you use them efficiently...Do you move all your RBs to the same location and swarm people with the RAS guys in 2-3 RBs? If you spread out your guys will only be attacking in groups of 5...
It's generally advisable to focus your units anyway, so yeah you want to gang up on enemy units with a bunch of yours where possible.
5) Why do most of these lists not have any Sang Priests? I've played with 10 man RAS units + Sang Priests and Sang Priests seem to give so much more to RAS units strengths.
Because it'd cost a fortune to give each unit a Priest and since you'll be spending most of your time driving around inside a Razorback you won't be getting shot at all that often, meaning you won't need FNP.
6) Those experience with fighting or playing with this list what is the best heavy support/ fire support for them? Devastators? I have 1 Baal Pred right now and 1 Reg Pred. I'm thinking of convering the Reg Pred to a Baal and using 2x Baal Preds with TLAC + HB sponsoons.
Rifleman Dreadnoughts (Dreads with two twin-linked autocannons). Normal Predators have a difficult time drawing line of sight to enemies past/over all the other friendly vehicles on the table. Baal Predators can do fine since they'll typically be very close to the enemy.
7) Are RAS units + your support fire (Baals/Devs) enough? Almost none of these lists have any Elites anywhere. Some run 1 Dreadnaught or so but why nothing else? Terminators in LR, DC in RBs?
Yes, they're enough. We're talking 30 Marines in 6 different vehicles driving around and shooting the enemy up, or charging them with nasty weapons as the situation dictates. Also, six squads of Assault Marines tend to cost a lot of points so you won't usually be able to afford Terminators. Also, Death Company suck, so don't take them.
8) Last question I think... How do these lists cover objectives with no truely great range in the small 5 man RAS units. Swap in some Sniper Scouts or what?
Six scoring units is more than enough in most cases.