If the containerized trees are exposed to the elements and you receive a reasonable amount of rainfall in winter, then no additional watering is required. If the containers are stored somewhere under cover, the soil should remain just barely moist to the touch so that might require a small amount of watering from time to time, depending on the quality and consistency of the potting mix.

IMO, pruning during the dormant season should be done in early winter (Nov/Dec.) rather than late winter (Feb/March) to avoid excessive bleeding. Sap in JM's typically starts moving early, often as early as January but for sure by February in milder climates. Summer pruning - June and July - is always an option. The adage is structural pruning in winter; thinning/shaping in summer. I personally prefer a light hand when it comes to pruning these trees - this is not a one time shot so small, selective shaping and branch removal can (and should) be extended over several seasons. You can always take more off later but you can't put it back on!! And I would have to say that if at any time one was thinking of removing as much as 20% of the tree, it is far too small to prune!! Or step back and reconsider your plan. These trees seldom need that much attention.

Thanks Gardengal as always for your Advice.100 Acres of these Lovely Maples would be very nice indeed.....