Like NoahZark's band, we tried to get something that could grow with the band.
We have a 16-channel Peavey mixing board. We always run 4 vocal mikes and a CD player (for break music), and sometimes acoustic guitar, electric piano, kick and/or snare. For the smaller clubs it is not necessary to mike the drums.
The board has a built-in (digital) reverb which is ok for now. The biggest complaint is that there's no reverb on the monitor channels.
We take a chance by going straight from the board to the Crown power amps. (We use high pass filters on the board but there's no limiter!

Not recommended!) The mains are powered by an 800 W/ch amp and the monitors are powered by a 300 W/ch amp. These are both overkill for the small venues we play.
We have two configurations for the mains. For larger venues we roll out the dual 15" 2-ways. Harbinger HX152, I think. (Hey, not everyone can afford JBL.

) For smaller venues we fly wedges on poles. (Don't remember what they are off hand; they're probably 1x12+horn.)
For the larger venues the wedges set on the floor to become monitors. For smaller venues we go with a single 1x10+horn monitor. (This monitor, Kustom KPC10M, has no real low freq. response but we're only sending vocals through it anyway so it works well enough.)
The problem with mixing boards is that they don't upgrade in a modular fashion. That is, if you start with a 4-channel board you can't add another 4 channels to it later on. I suppose you could get ridiculous and combine two 4-channel boards with a 2-channel stereo board.

In reality you have to sell the 4-channel board and buy an 8-channel. Then a 12-channel. Then a 16-channel. Seems like a pita to me.
Power amps share a similar fate: the upgrade path is via replacement. (Unless, for example, you add another mains amp to drive more cabs in order to increase loudness, but that just means more gear to haul.) However, you may be able to repurpose a power amp, for example, by using your old mains amp as your new monitors amp.
If you get a powered mixer then you'll have to replace the whole thing if you outgrow either the mixer
or the power amp(s). I've used these in the past and I have a personal bias against them. They can be convenient in terms of size, weight and simplicity, though.
Cabs are at least a little more flexible. If you start with 1x15+horn mains you can always add another pair of 1x15 (or maybe 1x18) subs later on to at least approach the loudness of larger 2x15+horn cabs (if not the same frequency response).
Powered cabs, IMO, aren't as flexible. They're like powered mixers in that they combine two functional units in one box: power amp and cab. If you outgrow the power amp you have to replace the whole unit. Although, as above with passive cabs, you could add powered subs later on in a modular fashion. My other personal bias against powered cabs is their weight. However having watched a DJ use them I did appreciate the way they simplify hooking up the whole PA system, not unlike when using a powered mixer.
So to the OP (if he's still around) if you're just starting out and playing smaller clubs and money is an issue (isn't it always?) then don't go out and get a really big PA. Remember, the larger venues will probably have a house PA and if you get a huge outdoor gig without a PA (!) you can always negotiate the price of renting a PA into your fee.
Again, for the smaller clubs you'll probably just run vocals through your PA. Unless you want to use in-ear monitors (IEM) but that's a whole 'nother story!

If all the guitars are running full stacks then, yes, the drums may need to be miked in order to keep up. But then the band will be so loud you'll drive your audience away with burst eardrums.

So, yeah, you'll probably just want to run vocals through your PA. (And leave the full stacks at home, too.)
You don't want to err in the other direction and get a system that isn't loud enough, either. It seems to me that the low cost PA packages aren't loud enough for a band. For a singer/guitarist in a coffee shop, maybe, but especially not for a rock or metal band. For example, if you get a 100 W system with 1x10 mains it probably won't be loud enough.
A good idea would be to frequent the venues you will be playing to see what other bands are using. Try to catch them on a break, explain that you're a fellow musician, and briefly ask them if they think their PA is too soft/loud and what their likes/dislikes are. This should give you a better picture of what your band will need.