On the first point, the issue is in theatre tank numbers. More tanks sent to Greece doesn't help Crete (or North Africa)Actually, more tanks will be in play, as the Valiant started production in February 1940, rather than the middle of the year, plus LMS is producing Valiants, rather than struggling with Covenanters (which, according to this site, didn't start serious production until 1941), so that's another company that's going to be months ahead on production over OTL.
Depends who (if anyone) the Germans send over (someone other than Rommel might not attack). And even if they do attack, having Valentines at El Agheila and Brega might stop the German advance.
More tanks might halt the Germans earlier if they were sent to North Africa (likely) but it won't help them enough to take North Africa without the resources spent on Greece.