If I have say 5 different items. all of which (this is all hypothetical) give +, I chose the highest +. HOWEVER my question is everything else those items do. Say 3 of them give me rerolls on attack, do I get all 3 rerolls? or do they not stack either?
This applies to many other item combos (its been a month since we played, but we might be playing again next week.) Like getting +1 to a roll, or anything else
Yes, having multiple items that give a bonus to a stat do not stack -- choose the one with the highest bonus, as you said.
As for other effects, you can use as many of those as you like. You could use the secondary effects from a Bull Whip, Axe, and Shotgun all in the same combat.
If you can manage to get three items that give you a reroll (e.g. Lucky Rabbit's Foot, Bull Whip, and an Axe), you can get all 3 of your rerolls.