Small sound install advice

Seated?... then why not smaller boxes down the length and a pair of large boxes at the end (where you have a stage?)

My personal opinion is to not to use 15+HF boxes. Never really liked the way they reproduce vocals. Late 2x installed I did I had flown double 6.5+HF boxes and 15"s scattered around so that the bass wasn't all blasted from one place so the over all volume could be kept down.

What not aim for 12+HF and dump 4x 18" reflex under the stage with possible 2x further 10+HF boxes half way down the hall so you're not cranking the stage boxes up and blasting the front row?

A stereo pair of 100v line with 4x speakers going down each side of the wall for non "party" stuff... and semi-installed system with tops on sticks with the subs permanently installed under stage. This way you can get the tops out for fun stuff (having a box on each side of the stage with a speakon socket and a 3m patch lead to go from wall to top box) that way all the amps/processing can be racked with a radio Mic system all racked together with the mixer not far away on a snake. This should make you fairly versatile as you could have a second set of wall mounted speakon boxes at the other end should you want the top boxes there for other things...

I'm just trying to make it more plug and play so you just move minimal hardware but using a centralised rack and with the mixer on a snake you should be able to keep most people happy with its use.

The 100v line system in place would be ideal for TED talks and town meetings... and when the fun starts switch over to the larger system all from the same rack And processing station.

Good chance to sell the old gear here and add to the budget, but simple boxes on sticks I don't believe is the answer... you just end up with the front row telling you to turn it down and the back row asking you to turn it up...

Your original suggestion probably isn't far off, other than I'd echo the advice to give the dBx Driverack a miss.  Either look out for a used BSS/XTA unit or dBMark probably offer the best value for new.

Some of the comments about 15" tops not doing vocals and distributed system being better but realistically, if you go for decent boxes (e.g. PS15's, not the X15) and get the position and angle of them right, you'll be fine.  Lots of small theatres run exactly that.  If you decide you need something more distributed later, a pair of smaller (8") boxes halfway down the room would help but then you're into needing to set up delays, more amp channels etc.  On a small budget it's best to concentrate on buying a few good bits of kit than lots of budget gear.

If you go down the 15" mid-top route, make sure you choose something with a large format compression driver (1.4" or 2" exit) because the lower crossover point helps to avoid the hole in the midrange you get with a 15"+1" 'Disco' box.

The EV amp would be ok but there are plenty of options that give similar performance.

There are almost certainly some bargains to be had on the second hand market if you know what you're looking for.

For example, on https://www.facebook.com/groups/nationalprolightingandsoundswapshop/ there is currently a DB system of 2 active 18" subs, 2 active 2x12" mid-tops for under £3k.  Weakest link in that is probably the 1" compression driver but maybe not a ridiculous option.

Which is where things like the PS15's with the dedicated controller make a lot of sense.  Can be set up to be fairly idiot proof.

I far prefer my twin 12" boxes for their midrange than my 15"+1.4", however for the majority of the gigs I do, the 15" boxes do a perfectly adequate job.