Hi Cik: I don't have much more time to comment on for now but a quick look at your list leads me to think that you only have 5 formations on the table? That's a very low amount for 2.5k; I would suggest that the spacecraft is a waste of points and that you should concentrate on having a larger number of smaller formations...with the models in that list I'd suggest something like:

Incompertus, 1505 POINTS
Ghazgkhull Thraka's War Horde (Epic UK v100909)
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WARBAND [315]
2 Nobz, 6 Boyz, 2 Grotz, Battlefortress

WARBAND [315]
2 Nobz, 6 Boyz, 2 Grotz, Battlefortress

MEKBOY STOMPAMOB [475]
3 Stompa, Supa Stompa

STORMBOYZ WARHORDE [150]
6 Commandos

WARBAND [250]
2 Nobz, 6 Boyz, 2 Grotz, 2 Killa Kan

LANDA [200]

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That gives you another 795pts to spend on stuff like blitz brigades with oddboyz and flakwagons, and maybe another warband with a zzap gun in it to sit on and protect an objective. Consider:

WARBAND [275]
2 Nobz, 6 Boyz, 2 Grotz, Big Gun, Oddboy (Zzap Gun)

BLITZ BRIGADE (BIG) [350]
2 Oddboy (soopa guns), 4 Flakwagon, 4 Gunwagon

BLITZ BRIGADE [200]
2 Flakwagon, 2 Gunwagon, Oddboy (zzap Gun)

Which would take you up to 2530pts so you'd have to save 30pts somewhere but perhaps you could change the boyz mob with zzap gun into a mekboy gunz mob instead and spend the spare pts upgrading other formations. THat gives you 9 activations over his 7 so if you're careful you can save your hard hitting weapons till last.

Stompas can't be cover for infantry behind them. However, if you put infantry in base to base contact with AV (up to two per vehicle), then the enemy suffers the -1 cover to hit modifier.
The infantry don't get a cover save though from contacting an AV, only the minus 1 to hit.