Hello Drummerboy2, and welcome on board
2245H+2123+TPL-150 looks like a nice combo with lots of potential (and of course lots of pitfalls as already pointed out).
Not sure about the MCM woofer tho...
The 2245H is a very good and versatile (sub)woofer, and you can replicate the 4345 tuning (280L @29Hz IIRC).
If you go the 2245H+2123H route, you should be able to find plenty of info on active solutions for the ~300Hz crossover.
This is a tricky frequency range to measure, so you better rely on proven solutions there.
One advice regarding that range: keep the woofer and mid woofer on the same baffle to avoid having two different baffle steps in effect around the crossover frequency.
Also try to get the 2245H off the floor to avoid triggering vertical modes in the >100hz range (dust cap at around 1/4 of the ceiling hight is often a good solution).
The 2123H/TPL transition will be unknown territory (around here at least, maybe some have done that on the diyaudio forum), but at ~1200Hz this crossover will be much easier to measure and dial, and with a bit of patience and knowledge you should be a able to get a theoretically perfect acoustical crossover using only in house measurements.
You might need to use the horn on the TPL to get it down to 1200Hz and -more importantly- match directivity with the 2123H.