#1
I've got a $600 budget for an amp head and about the same amount for a cab (but I can save up more).

I'm interested in the:

-Ampeg B2RE Bass Head
http://www.guitarcenter.com/shop/product/buy_ampeg_b2re_rack_bass_head?full_sku=103128344

-Gallien-Krueger 700RB-II Bass Head
http://www.guitarcenter.com/shop/product/buy_gallienkrueger_700rbii_bass_head?full_sku=102343894

-Gallien-Krueger Backline 600 Bass Head
http://www.guitarcenter.com/shop/product/buy_gallienkrueger_backline_600_bass_head?full_sku=103056032

I'm looking for a variety of tone, not to fussed about the volume though, tone is more important at the moment. I'm not sure about what cab yet though.
#2
Out of those, I'd definetly go with the Gallien-Krueger 700RB-II. I've heard great things about it. With a $600 cab budget, I'd look at some 4x10s. Look on your local Craigslist, I often see people selling bass cabs on there for great deals.
#3
those are solid state arent they? i know the ampeg is but not sure about the GKs, think they are
#5
^ You'd be surprised. Graphic EQ's rock, but a well made active parametric EQ can be just as good.

EDIT: Also, a graphic EQ won't make your amp or bass sound exactly like another amp/bass.
"You can practice to attain knowledge, but you can't practice to attain wisdom." - Herbie Hancock