Since it might not be clear to you, what Dave is saying is that CM's flower on the ends of the growth from this year - one of the reasons people get away with, and perpetuate the "crape murder' which is what you get told NOT TO DO by members of GW - which is why he suggests waiting until after flowering or doing your trimming in spring so as not to lose this summer's flowers. You might by now be able to see flower buds forming at the branch tips and be able to decide if you want to remove the most wayward branches even so, losing the flowers. If the branches aren't too much in the way, my inclination would be to wait 'til they flower and then deal with them. IF they ARE in the way, shorten them back until they aren't, or, if you want a tree-form, take them off at the trunk. As Esh Ga says, you can grow either a tree-form or a bush-form CM. Some of the newer, dwarf cultivars can, and should, be grown as bushes and look very nice. If you know, and tell us what cultivar you have, you can get more directed advice as to whether to trim up the trunk, or leave it as a bush. In any case, you can grow most cultivars as bushes and/or in pots for several years, so there is no urgency, other than your expectations of what you want this CM to look like. If it isn't one of the dwarf cultivars, then eventually it may outgrow the pot and the space on your deck, and need to be planted in the ground. For now, though, it looks to be quite happy and healthy where it is.

Now is the perfect time to prune . Your trees could definitely use some help . It might be more beneficial to prune some old growth this year and some next year to avoid shocking the largest tree too much . I would leave the branches that have grafted together . A large wound in the bark will allow entry of insects and disease . Crapes seem to look best when they have 3 ,5, or 7 main trunks . That might be a good place to start . You will want to avoid cutting them to the ground . Severe pruning or topping can stimulate basal sprouting which can become a constant nuisance, requiring regular removal . Well-established plants are extremely drought tolerant and have low fertility requirements, although they respond to fertilizer and water with lush growth. You will find more info here - Here is a link that might be useful: Crape Myrtle in Florida

You can cut it back at the 7 ft size and it will put up new growth and the branching will be lower than it is right now. It will put up lots of new branching and if you remove most of those when they are young and just have 2 or 3 branches you can let those grow and prune them back and selectively keep a few of those branches. That way it is branching and not like an arm with the fingers cut off. If you google "how to prune over grown crepe myrtle" you will get lots of help. Most suggest doing it over several years. Some suggest cutting it back to the ground and letting it start over.

The most beneficial pruning involves eliminating crossing, inward growing, and rubbing branches....and that's it. When those branches are pruned, they need to be cut to an outward growing branch. A nicely formed crape will need very little, if any, pruning. That will open the plant to improved sunlight penetration and air circulation which is always good for flower production. Topping, chopping is never a good idea.