So I already upgraded it to +3 and I want to know when it's best to stop Upgrading it? Because I don't want to grind for a long time just go down the floor after exploring it all. (I've won twice now, I don't know of this helps saying it incase it is helful)
As a mage, +3 is probably a fair stopping point, maybe +5 if you really want the higher end equipment. You need the upgrades for your staff.
For other classes, it depends. As a huntress, I’ll often stop at +11 or +13, depending on what level I found it at. Farming consumables and higher end equipment can be super fun! A +13 ring of wealth will provide +7 armor and weapons, which can easily be game winners. The higher level also will provide several scrolls of transmutation that I often use after dwarf king to get the ring that I want.