trpullen's point is very valid. If it sounds like crap to the singer it will hurt the perfrmance of his singing. All music but especially vocals are effected my confidence/emotion. If you hear your self sounding like crap it can build in your brain.
300 watts at 8ohm is not bad for very small quiet venues. I would think you could use that for the mains in that situation. Monitors too,,, I would say that would be a stretch.
I agree with trpullen that 8inch monitors would never even cross my mind to purchase. I can't emagine getting a good sound out of them. Take a look at the carvin web site. I got a pair of 12inch with a horn monitors years back for $350.00 with covers and really nice cables. I have been very happy with them.

and I feel for the money that they are a great deal.
As far as out front goes.. In my opinion you will never have a good clean sound with out some drastic changes. (this is if you play at any volume) I would get a board, a snake (so that you can mix out front) I would mic everything on stage except maybe the bass where you could run a direct line, I would put it all through the mains, from a minimal point of view I would want some top cab's 15inch and horn (bi-ampable!!!) and a set of subs to throw under them. Then you get an active crossover, run from the board mono through a 31 band eq then to a 3 way crossover (if you buy one get a 4 way for the extra $30). Have the crossover run into two stereo amps (by that I mean 4 mono amps) for one of the amps you need some real poop, a 800 or 1000 watt amp at 4 ohms at least. run below 200 hz into one side of the amp and out into the subs, run from 200hz to 1250hz or so in to the other side of the big amp and out to the 15's in your top cabs, Then take another amp (could be smaller 400 or 500 watts). run above 1250hz out into one side of the smaller amp and out to the horns in your top cab's, then use the other side of the smaller amp to power your monitors (running out of a aux send) Then you can dial in how much of what you want in the monitors by adjusting the aux send on that channel.
Now for the big one. Get a sound man whos work you have heard and like!!!!! Have him come in and help with the set up (at home first if possible). And always have someone other than a member of the band mix you (A sound man). Then you will be on the way to a good sound, hopefully
This is just about how I run. I left out some other equipment you could live with out, actually you could live without the sub's for now. But I would run the mains bi-amped anyway. You would be amazed how much an active crossover and the equipment to go with it can clean up your sound.
Just my opinion
later
F.S.