I'd like to clarify something about allying: can Chaos-related armies be put together under Bound rules? For example, the current starter kit has Space Marines vs cultists. Space Marines can be allied with Sisters, so their side of the kit could indeed serve as a starter for an Imperial army. What about the cultist? Could I add Chaos Marines to them later, as well as Demons?
Cultists are a troop choice in the Chaos Space Marines codex. If I remember the Allies Matrix offhand, Chaos Marines can ally with Deamons freely, and are distrusted allies with Orks and Dark Eldar. This means they'll kinda work together, but they don't trust each other.
The starter set you're talking about is the Dark Vengence one. That was brought out for 6th edition, and its not bad for the money. You could probably convert the Dark Angels up as Chaos, and you'd have the beginings of a decent force there. I'm not sure if it has the 7th ed rulebook in it though. If it's been updated to 7th, then yeah, it's a good buy.
Lord (HQ choice)
Champion (could do as a Lord or go with the Chosen)
2 small units of cultists (Troops)
Hellbrute (aka Dreadnought) (Heavy Support)
Officer and Librarian (psyker) (HQs)
Bikes (Fast attack)
Squad of Marines (Troops)
The models are all snap together ones, so they're not as posable as regular ones, but their simplicity makes them good for absolute beginners, which is what the set is marketed towards.
BTW. How big are armies used in WH40K, on average? I found one instructional video for beginners on Youtube and it featured 10 Marines vs. 20 Tyranids. And the battle seemed to be over in... minutes? A few rounds and the game was over. Is that typical size of armies, or are they larger?
10 marines, depending on what they have probably come in at about 200 points.
The default tournament sized around here is 1750 - 2000 points. A 2000 point game, assuming you're not playing horde armies and are reasonably familiar with the rules, will take about 2 hours.
The largest game I ever played was a 7 a side Apocalypse game, where we had about 40,000 points on each side. It was the Battle for the Emperors Palace, the climax of our Horus Heresy campaign, and played out over an entire weekend. Several titans and superheavies on each side, scores of tanks and hundreds, if not thousands, of infantry models :)
Most games will last about 5-7 turns before they end.
Also, if I may ask: any experience with paints? I browsed GW store and they seem to have different sets of paints: basic, layer, shades, dry (). Are all of them necessary?
Not to start with. My basic paint job consists of
Bolt gun metal silver on the weapons and the joins of the armour
A dot of red on the helmet eye lens
Green on the base
Add some flock to the base to look like grass
I'm done :)
Shading and drybrushing are more advanced painting techniques. The models will look lots better, but they're not things you need to worry about right away.