You only need to trim if one is too low for where you want it. Don't have to walk under it, don' trim. Yes, you trim dead branches. Yours looks very well shaped.

It is perfectly true that many young decurrent trees (shade trees that grow without a defined leader) do need structural pruning to encourage a healthy growth habit. Generally it involves subordinate pruning with two (or more) strongly competing upward growing branches - what passes for 'leaders' in other tree forms - 'Autumn Blaze' is well known for developing in this manner. But there doesn't seem to be any reason for doing so in this case. I don't see any indication of co-dominant growth patterns.

As time goes on, you may want to remove some lower growing branches just for easy clearance when mowing, etc. and to balance the branching around the tree. And you can always remove any dead or damaged branches or stems and those that cross or conflict with others. btw, it is far easier, better for developing growth and with less stress on the tree do any necessary pruning while it is is still young. IOW, prune before anything becomes too unwieldy, although I do not see a strong need for any serious pruning now.

Structural training of young shade trees.

Except perhaps for that competing lead to the right of the main stem (second picture) I'd leave the tree alone, as this is a 'Jeffersred'. With this one you eventually get a comparatively tidy outline but the inside of the tree can be wild, with numerous branches that don't all line up neatly.

Unless it is branching too low. At this stage I would tip back the too low branches for some years, while the rest of the crown gets bigger, before finally cutting these off completely. Right now the lowermost branches make up quite a bit of the total top area.

Embothrium, when you establish one lead for the tree, do you completely cut off the competing lead? Or just trim it back a ways?

In this instance I would cut off that one secondary vertical completely. Tree was already trained to have a single dominant stem - and this other one started as a water sprout on a low branch - so I suggested cutting it out. Otherwise a maple of this type might often produce multiple vertical trunks of similar size to one another eventually, but for now I would continue with the existing basic structure.