I have 6 tomato plants of different varieties grown in planters outdoors. I have heard that there is a recommended limit to the number of trusses (bunches of fruit or number of branches bearing fruit) on a plant after which you should crop the top of the plant. I believe this is to focus growth on the remaining fruit.
Is this correct? What is the number of bunches/branches I should limit my plants to?
The "recommended limit" depends on who you talk to. I think it comes down to how obsessed you want to be with managing your tomatoes.
In "How should I prune my vine tomatos?", there's a video in which they suggest you should limit growth to the main branch and one sucker.
In one of Eliot Coleman's books, he talks about growing a single vine up to the roof supports in his greenhouse (8' high).
In my Garden Way book on tomatoes, the author is skeptical of any pruning at all. (Too much work for not enough additional yield.) Instead he is in favor of "topping" if the plants get too "dense and green". This involves snipping out some vines with shears or slashing some off with a sickle.
My personal experience is that pruning helps. Also, staking + weaving works better than caging. I'm a pruner (not obsessively -- sometimes I get behind), and I've found that it's easier to prune staked tomatoes than caged tomatoes. Sometimes they get out of control, and I still get a crop. The year that I had an 8' high wall of tomato plants was probably my lowest yielding year -- I did almost no pruning and the vines were out of control, all veg/no fruit. This year I aggressively pruned my staked cherry tomatoes and it looks like we're going to have an excellent crop. Lastly, the combination of wider spacing between plants and regular pruning helps with air circulation and keeps down disease.
