imo, you dont want to just feed him all he will eat, especially if feeding crickets. he should be on a controlled diet of about 1/2 of his potential food intake. excessive feeding can lead to impaction, prolapse or other issues.
as far as the co-habitation issue, there is no end all answer. no 2 xanths are alike, they all have their own personalities and set of issues (just like people). cohabitating a m/f pair is never recommended in normal size cham cages. cohabitating f/f pairs can sometimes work, but the potential problems and resulting stress can be very hard for a novice keeper to recognize in time to prevent problems, so imo, its never a good idea to cohabitate unless you are very confident of your husbandry. i had a pair of females that co habitated seemingly well for about 6 mths after that it was clear that the situation was causing problems. its entirely possible it was causing problems from the get-go and i just didnt have the exp to recognize it.
imo, as far as xanths are concerned, attempts at cohabitation are best left to experienced keepers with large outdoor enclosures, and lots of extra resources, (like backup cages/equip, $ for vet bills etc.)
as far as the basking issue how are you measureing your temps? its very easy to be significantly off on basking spot temp measurement imo the only suitable way is by the use of a digital therm with a remote sender located in the sweet spot of the beam. the zilla hygro/therm for $20 is a great basking spot temp measure and a great cham husbandry tool overall. a incandescent uva 25-40 watt bulb in a small tight reflector should produce temps of lower 80's @ about 1' (basking spot-6-8" from the top of the cage with uva bulb in a narrow beam reflector about 4" above the top of the cage). what kind of bulb/reflector are you using for uva? just for the record, the temps are significantly lower just 3-4'' outside of the sweet spot. depending on how you measure temps, its entirely possible that your basking temps may be significantly higher than you realize. jmo
