I would examine the temporal aspects of your design. The way jittering works isn't all that obvious. It's useful to test various designs for statistical efficiency first. There's software for that "out there", though if your desired designs don't fit the general setup of those packages, you'd have to write some code on your own.
For example, suppose you have two types of visual stimuli, A and B, and fixation ("fix"), and the pattern is
A-B-fix-A-B-fix-A-B-fix-...
i.e. the order is always the same. Then you're not going to do too well unless you use what's really a "single trial" design (ie pretty long ITIs/ISIs).
Of course, maybe you already know all that; then the types of things you list would be reasonable to look at.
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