I agree with JZinCO. I don't think it would benefit individual plants to prune them.
However, cutting plants to 'hedge your bets' is a good idea. Here's what I mean: You get a new macro algae, and you don't know what its preferences are, regarding light, current, etc. So, you cut the plant into three equal parts, and plant them in three different areas of your tank, to see where it is happiest. I think this is a good strategy.
I don't think you will see a lot of growth until you feed your macros. If you don't want to add fish yet, you could just add fish food for now. Now is also a good time to build up a detrivore community and clean up crew. They will help convert the fish food into plant food.
It's a tricky game, at this young stage of your tank's life. You want to keep nutrients low, to discourage micro algae growth, but your macros need nutrients too. And just to make it even more tricky, micro algae are more efficient at nutrient uptake than macros! But you've got to 'drive' the system to get it to develop.
It's pretty tough to get a new tank going, without an algae phase. I see it as a necessary developmental phase of all aquariums. As I watched it unfold in my tank, I thought it appeared to be one part of a natural succession. The first colonizers are the bacteria, then cyanobacteria, then micros and finally macros.
One strategy from the fresh water plant folks is to plant a new tank heavily, so when nutrients rise, the plants are already in place, to take them up. I tried this strategy. I still got algae.