welcome,
in answer to your questions, around 1500 points is a good start for any army, base the army around two troop 1
HQ and any other elite units ,heavy support and fast attack. usually about 1
HQ, 2-3 Troops, 1-2 Fast attack, elite, and heavy support. The army list depends on units you like or want for there special abilities and weapons, or choose an army list for killing certain types of units, it all depends on your personal preference.
Any other questions you have about anything can be posted in the correctly named forum, thats why were here.