I'd do a half a box of borax at a time. After a couple of hours, retest and redose until you get it where you want it. Probably between 7.4-7.6 although anywhere between 7.2-7.8 is ok.

Regarding alk, it is going to take quite a bit of baking soda (like probably 15 or 16 lbs.) but you certainly don't want to put in that much at once. You can actually buy a big bag of baking soda at Walmart and also at Sam's Club, I think. I'd probably do a couple lbs. at a time. Take a few days to get it all in there. You add Borax and baking soda slowly through the skimmer while the pump is running. It is ok to add a dose of one right after the other with no problem.