I think the safe rule is not to exceed 50mg per day of any 17aa. That said, there's a lot of people out there that are using anadrol at 100 and 150mg per day and it's supposedly the most liver toxic of all.
I don't think it really matters if you take them both at the same time, as long as you keep it at or below 50mg ed. IMO, you'll be happier with the results if you do the dbol first four weeks and the winstrol second four weeks.
I've done oral-only cycles (always including dbol or anadrol) and been satisfied with the results. . .however, PCT is ESPECIALLY important with an oral-only cycle. You should probably have nolva or adex and clomid on had (keeping with oral-only theme).
Also, while on , use some tylers.