1. You can't really paint the entire model with an airbrush

It's just another tool, and an excellent one for basecoats, priming, object source lighting, gradients, and varnishing.
Files, sanding blocks, mouldline removers, hobby knife are all good.
2. Aie carumba. There will page pages on this bud. Short version -- it's your personal preference, pick a paint brand with the colors you want to paint. Specifically, for blood angels, Mephiston Red by Games Workshop is an awesome red; Vallejo, despite many great things, has a terrible red.
3. Well, if you want them painted to codex, it will be Mephiston Red (base), Evil Sunz Scarlet (layer), and Fire Dragon Bright (edge) as your "red colors". Agrax earthshade wash in the crevices.
For your basic theme, pretty much, red has to be there since they are "blood" angels
Death company are black, and one of the successor chapters are a darker shade of red, with black pieces. Black is a nice complimentary color without breaking the "death" theme, and cloth is a common theme in
BA units. Look at some of the Space Hulk stuff in my gallery to see what I mean.
4. No 32
mm resin bases yet. But there are lots of 25mm and 40mm resin bases; they are about $1 for 25mm and $2 for 40mm. Or you can make your own bases (using the included blanks). Just your preference.
5. Er.... "Yes"?

It depends how much time you wish to spend per model, and to what quality you want them, and what look you want.
6. You don't need any tools to pose the models. Everything except snapfits can be posed any way you like. You can use blue-
tac to test fit them.
I usually paint the head separately and assemble it when done. The other pieces, it depends on the model; I'll always at least partially assemble, but sometimes I'll paint various pieces separately and other times, I'll preassemble.
Which way you point the head actually makes a huge difference to the pose. The three most popular ways are: looking down the gun sight (aiming), square to the shoulders (at ready/standing guard), and looking the opposite direction as what the gun is pointed (looking behind). Looking the opposite direction looks good on solo-type models or sergeants, less so on troops because you don't want every unit to be looking backwards.
Keep in mind ever MPP troop kit has different lower torso poses; some will look more crouch-y, others will be standing tall, while others leaning forward. Mix them with the arm pairs to get the effect you want!