Hi Bart.
There is no need for the saw to run it almost perpendicular to the board, it may be faster but it also leaves a more rough edge, specially on plywood.
I've made a rough sketch so that you can see how it is done, once you try it you find that it actually helps a lot to cut straight, because when ripping the grain tends to dominate the saw making it drift, in this way as the saw has more surface within the cut it is easier to stay in the line. And as the saw has the stiff back the blade can't bend taking you out of line.
If the two gent saws have been tried to be sharpened, then just go for it with them, they do not look specially good to me, so all that you can loose is 4 $ and you can learn a lot.
You'll need a saw rake or make yourself one. And as per the the set, rip saws have none up to very little set. Crosscut ones have but if you have one of those saw setting pliers you can set the teeth easily and all with the same set.
You can do it Bart! I'm abosultely confident in your skill. Do get some documentation and give it a try with those gent saws, when you are happy with them go for the others. Use one of those magnifiers that one wears on the forehead or similar and go for it!