If the roses are budding they need to go out - you won't be able to hold them in the garage for 3(!) months after they have started developing new top growth. And then suddenly move them to full outdoor light. If you even have enough light in the garage for them to leaf out, grow shoots and bloom there, in the meantime.

Root pruning the maples right before bud break would make sense to me, because new roots will be made from the cut root ends immediately afterward.

You are root pruning to control size, as would be done with bonsai?

Root pruning of JM's can be done any time they are fully dormant, so now is fine. Also last frost date has nothing to do with when hardy woody plants can be brought back outside from winter protection. You want to do so gradually anyway, so when the temps warm up sufficiently (nights generally above freezing), you can bring them out during daytime hours, increasing the time they are out gradually until it is around the clock. You can always cover or bring inside overnight if very cold temps threaten.

The trees have been in the containers for quite a few years. The trees weren’t as robust as in years past. They need new soil and roots pruned.

The roses always bud early in my garage. They will eventually go outside, but not anytime soon. Lots of colds days still in the forecast.