i've been ascending every 2 weeks for the last...omg forever (I started 2 weekly ascentions in July and I ascend again tommorrow, then one more and i am done)
my advise is this, your mothership is pretty much a fixed stat, too expensive to increase the weapons/shield capacity just to ascend, so if its 500 bill...its 500 bill.
your attack should be roughly 1/3 of your defense, because the best way to increase rank is to have all stats equal (trust me i've tried att/def 50/50...) i do 2.5 T attack, 7.5 T def, utilise mercs here too. And as many UU as you can beg, steal or borrow, trained as AC level 28/29 because as has been said, an AC is 50% higher ranked than a covert.
edited to add, I just finished a rough guide to ascending, for the DDE Empire forum, so if anyone wants a copy, grab me on msn and i'll send it in a document xxx
aku-lizzy@live.co.uk