Establishing Pre-Bonsai Tropical Starters in 5a

Hello I recently purchased a number of small tropical* prebonsai all of which are very young and I’d like to work developing their primary structure. They’ve been temporarily repotted into small containers sitting on a window but I’d like to repot them into larger containers outside once temps improve but I have a couple of questions:

First, outdoor temps are still too cold to leave these plants outside overnight. I’m in zone 5a of the US Midwest where lows are in the 40’s. Will it have an adverse reaction on the trees to shuffle them outside during the day, where temps could be anywhere between 50-70, and them bring them back inside at night to an indoor temp of 69-71?

Second, I have ample outdoor space for these trees but will be more space-limited when these plants need to come back inside during the fall. If my immediate goal with these trees is primary trunk development, should I plan for a couple years of repotting them in the largest possible containers I have outdoors for spring/summer, then repot into more compact containers to bring inside for the fall/winter? Or should I choose pots with the largest possible volume I can consistently keep both indoors/outdoors to avoid frequent repots?

*dwarf powderpuff, melon seed ficus, mahogany, water jasmine, and fukien tea

I am no expert but my understanding is that tropicals are repotted in the SUMMER when they are actively growing

So the cycle is different than with outdoor bonsai.
What I have read is anything below 50 degrees could lead to death/damage so to be on the safe side I keep mine inside in Northern Vermont until we are above 60 degrees.

I think you could shuffle them in and out all spring keeping 50 as your absolute min temp.

As far as pot size for repotting I think you want to move up in moderate steps letting it fill the container with new roots before moving up in size.

It has worked for my ficus, and fukiens I repot in July which is my warmest month.