Hmmm... this is going to be more difficult than i thought

Lots of questions ahead!
The griffons were only really there because I was planning to use the FW Medusas as them, so can easily be dropped. I do like the amount of firepower one of the infantry coys would throw out tho!
I do not particularly like the GW siege models, not even the Ragnaroks so I would have to find an alternative! They seem pretty lacklustre on paper to me, but I am probably wrong.
Also light tanks or Rough Riders? Both seem fragile but useful for objective grabbing.
On the fortified positions, is 1 really enough? It seems rather skimpy for a siege force, do you not want just about all of you infantry in trenches or am I missing something? I had gone with three to give me a solid front line, with another set as a second line around the screened with RRider artillery etc... I agree that the razorwire seems great, almost better than the trenches!

Would you suggest Tbolts AND AA guns? Or just AA guns? They seem quite delicate, but have good range.
I am looking to get a list pretty much pinned down before I start buying stuff, so anything and everything can change!
Thanks guys