I've been wanting to go with separate components but a receiver isn't out of the question.
I have very little knowledge of speaker setups so any help will be appreciated
Budget is $1200 ish
Looks like your Mosaics are a fairly tough load to drive. (I don't know for sure since there's no impedance / electrical phase graph I can find; the ML Montages may be similar - http://www.stereophile.com/content/martinlogan-montage-loudspeaker-measurements) You'll probably want an amp that's stable (that is, has a power output rating) into a 4 ohm load. Perhaps favor high current designs, if you tend to push the volume up.
Separates can offer better performance, but there are many well designed and well regarded integrated amplifiers that can offer the same, if not better, performance.
Outlaw Audio RR 2150 ($699)
NAD C356BEE ($799)
Marantz PM8004 ($999)
Creek Evolution 50A ($1195)
If you're committed to separates, I've heard good things about Emotiva. The USP-1 stereo preamp is $449 while the XPA-200 stereo power amp is $499. They also offer a 30-day no-hassle return policy since they sell direct.
Hope this helps!