Again, thanks for all the replies. I did a little more research into my questions, and the following summarizes the responses and my observations:
Destroying high level caps gives the most experience points (xp), and from there it pretty much scales by ship tier. Structures also give relatively small xp. Destroying planets does not give xp. Each item's info card will list how much xp is delivered when you hover your cursor over it. Nothing else gives, or takes away xp. If 2 Cap ships are present, they will share, or split xp in half.
Planet Militia give the same xp as TEC counterparts. Pirates, due to their lack of shielding, give about half the xp of their buildable counterparts.
Destroying Capital ships gives: up to 580 points for a level 10, down to 60 points for a level 1. (lvl 6 = 260xp, lvl 2 = 80xp)
--- Ships--- --Pirates--- --Structures--
HCs .............100 .. Corsair......50
Adv Carrier...100
TEC Carrier....80 .. Cutthroat..35 .. Hanger.....75
Siege.............65 .. Pillager.....30
Flak...............50 .. Reaper.....25 .. Def. Plat...50
LRF, Supp.......30
L Frigate.........30 .. Rouge......15 .. Labs, etc..25 (Factories/Refineries/Trade/Culture)
Colony, Scout.20 .. Extractor..20
Constructor....10
Bomber...........6
Trade/Cargo....5
Fighter............3