As far as I know there is nothing stopping you from fielding a fully stompa mob based army.
Thinking of my experiences with stompa mobs I would say the following:
1) Setting the mobs to be really shooty seems a good idea but you really need to sustain fire to hit anything, leading to actvation issues. Ive never tried a CC kitted mob, but imagine the sped would limit them getting into combat on your terms.
2) Supa stompas are great value for money, but the soppa gun is not as effective as a supa zapp gun- particularly if doubling where your to hit goes down to 5+/6+. Ive dropped a 6BP MW barage on a clumped marine tac formation and failed to hit ANYTHING. On sustain fire though these things are REALLY mean
3) Dreads are worth their weight in gold for protecting your stompas from assaults and taking BM.
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If I were planning on a stompa based army I would go for: -2-3 shooty supa stompa mobs (ie 3-4stompas, 1 supa stompa plus some flak wagons and maybe killa kans for shielding).
- ~3-4 assault stompa mobs loaded with dreads and possibly a couple flak wagons.
Double the supa stompa mobs to establish a base of fire then sustain in turns 2-3. You should get ~2 out of three mobs passing the sustain action each turn (particularly if using reroll). The assault mobs would then double into assault range and take the objectives.
I would also have some KOS to act as a fast reserve and aid in the assault on objectives. One of the problems I have had with stompa mobs is that they can be easily outflanked and out maneuvered. I have started Keeping a fast asault mob like a KOS or stormboys mob nearby to help them out.
EDIT- should probably add that since a squad of terminators managed to shred a large-ish stompa formation of mine ive become rather paranoid about stompas being assaulted- its a most un-orky way to act
