For transplanting something delicate, I often take a great deal of the soil around the rootball with the plant. Just a big hunk all around the plant in the hopes that so few roots are disturbed that the plant doesn't figure out it had been moved. I then dig a hole about the same size as the huge hunk of soil (with the plant embedded in the middle). I gently place the plant in the hole, fill in the gaps with extra soil, then step lightly (or, maybe I stomp) on the perimeter to firm the contact between the old and new dirt and finally give it a good bucket of water. Every plant is different so no guarantees of blooms as a change in sunlight, water drainage, etc. can also contribute to the adjustment period. Good luck!

My Baptisia ("Purple Smoke") thrives in a climate closer to that of nanasflowers, and it's in average soil (not especially well-draining). B. australis and its hybrids are tough, adaptable plants. Interestingly, you see advice about not "disturbing" the roots, but evidently some abuse is well-tolerated. I'm especially fond of "Purple Smoke" for its mass of attractive foliage which is ornamental throughout the season, and striking even after a hard freeze, turning near-black which contrasts nicely with volunteer goldenrod.

Scott, your decision on pot size should be based on your facility that will provide light for the plants. If you only have 1-3 of each of the varieties mentioned you likely could transplant into quart pots and still fit under 4 shoplights but if you have more plants I would keep the plant "Footprint" smaller by first using smaller pots. I typically transplant from trays to 48 cell packs ( 48 plants in a 10"×20" tray). That is typically a 6 to 7 fold increase in footprint. After 3 to 4 weeks when I transplant from cell packs to 4" pots my footprint is so big that plants fill a small greenhouse. If you are transplanting into gallon or larger pots you probably should be moving plants to their final destination.

Unless you are in the Southern hemisphere this is just about the worst time to transplant leafed out rhubarb. Those big leaves are transpiring like crazy and the disturbed roots will not be taken up much water at first. Shade it, give it ample water and cross your fingers. In the ground it is hard to overwater it. It will be very grateful for rain, not resentful.