Black Shark at 50 was fine. But Gut/poly is insane in the Tour 16x18. I also found adding a leather grip increased the feel and added a little weight in the handle, and a little lead tape at 12 transforms the frame. I would guess you could go a little lower with Black Shark (but not much) I think the Pro line 18 would break pretty easy...but while it's in there, it should be a ridiculous spin frame

If you hit with a significant amount of force, it is doomed to break in under 4-5 hours IMO. 18 Gauge seems like it is meant for 18x20 frames that need a little more openness. The Tour 16x18 is wide open and the ports allow a lot of string movement (still, one of my favorite frames). It will murder 18 gauge anything
I wouldn't say the ports make everything super goofy. But between the ports and the low flex, I have found stiff/crisp strings to play very well in it. But if you want the most comfortable frame ever, put a soft string in the Tour 16x18. Once you get used to that frame, it is magical. You might want to grab a set of grommets or another one if you plan on sticking with it. Prince is sold out of them (unless you are grip 1), so once the retailers deplete their stock, it will be gone

Enjoy your new stick!!! It is one of the great ones!!