I'd inject as often as you need to, and no more than that. I realize that's an ambiguous declaration, but it's offered in response to your question about an EOD protocol. I don't know, and nobody else really does. Twice weekly shots, as you're planning, may well be successful. If they're not, it will be necessary to check what total and free testosterone levels were achieved on your every 3.5 day schedule. You and your doctor will have to look at your estradiol - is it at a comfortable level, or must attention be paid? HCG - if it's on the agenda - has to be weighed.
I inject 16mg of enanthate every morning; that's my third injection protocol. It works, spectacularly well. But we arrived here in a step-by-step manner. Many guys don't need to inject more frequently than twice a week. If it turns out you do, you'll have plenty of data to draw on.