Now come to the point where I like to build my own speakers.
Welcome to AC

If one have a hi sensitivity speaker as 100dB or more(rare) and bening impedance curve there is no much things to upgrade to have a great system.
A hi efficiency speaker will allow you take vantage from inexpensive small tube amps which have great sound quality and save a lot of money:
http://www.glowinthedarkaudio.com/amps.htmlIn case of sole FR drivers speakers as Lii Audio F15 or F18 OB will have less cost yet hence no crossover, no driver sensitivity loss(1dB), no enclosure and no retail price:
http://www.glowinthedarkaudio.com/speakers.htmlOthers small amps suited to hi efficiency speakers are First Watt(expensive), Chip-amps and GaN-FET amps.
This is a inexpensive DIY project from an AC member,
It have only four (4) parts:
Eminence Alpha15A + 4.7mH + Visaton B200 and a MDF baffle.

Other option are the Lii Audio F15 FR driver $399/pair, not each.
Here Decware OB with the Lii Audio F15 driver:

If one have a woodworker is possible try the Lii Audio F15($399/Pair, pair not each) 97dB/8Ω and benign impedance curve suited to OB or Bass Reflex box or the F18($540/pair), no Crossover, no Tweeter beaming, no Phase rotation, no driver sensitivity loss, no Harmonics loss, no Retail price.
http://www.glowinthedarkaudio.com/lii-audio-f18.html
My personal choice is the Lii F18 in Single Driver configuration, but if you make question of own a 2-Way speaker you may want a bigger woofer than the Alpha15A, so there are W18 inches and W21 inches from Lii Song Audio, personally I dont like these two VCs woofers, they are hard to drive with a small tube amp, they have two Voice Coils.
https://www.lii-audio.com/product/w-18/
https://www.lii-audio.com/product/w21/