Yeah, a small mixer if you just need basic EQ and reverb, or, if you need more proccessing, a XR12 that lets you use full compressor, gates, EQ, effects (chorus, reverb, delay, different compressor, enhancer, exciter...). If you use a little looper, it´s easy to take a walk on the audience space to tweak the overall sound (a simple Zoom G1 would do the trick, plus you´d have tuner and additional EQ/effects if needed, for dirt cheap and small size).
Then, a couple speakers (not necessarily top tier ones). Altos are good enough, and if you´re exquisite, they say the QSC CB10 sound stellar. It seems they´re the new favourites in theacousticguitarforum.
Regarding the guitar, I´d just use one with a JJB pickup. Add a little compression and 1kHz small cut to remove honkyness. Those pickups (K&K style) sound very good, are passive, avoid all knobs, cuts, batteries or extra weight in the guitar and are cheaper than K&Ks.
Yesterday I was testing different preamps at high volume with my JJB equiped guitar. All of them sound very good just compressing and EQing from the mixer (Midas MR18). Fishman Platinum Pro/EQ, Bo Hansen active DI, Jack Orman JFet buffers (AMZ musique web... dirt cheap, but DIY), Pumpernickel compressor OPamp buffer, Nano Cortex with captures from several preamps (Grace Alix, Neve, Baggs Venue DI, Baggs PADI, Bodyrez) and even the buffer in the Boss MS-3. They all can sound similarly good with just small tweaks. You only need to be from 500 kOhm impedance and up, and slightly tweak to get a good tone.
I think a good buffer, some device to compress and EQ (be it the mixer or a little multieffects), and a couple speakers... and call it a day. I wouldn´t use acoustic amps.
