RE: MY KADET LT-40 BUILD
Hmmmm... In this case, I suggest just leaving the gap. Make sure the tip is glued in securely, then press on. The "pothole" will be covered by the covering, so it's not really a big issue.
As far as the joint between the wingtip and tip rib, consider it a learning experience. I like to bevel them and check the fit before doing any gluing (goes for all parts - always do a "dry fit" ) You'll be able to sand whatever sticks out when you do the final sanding on the wing. I wouldn't worry too much about the wingtip, it doesn't carry much load, and minor glitches are mainly asthetic.
I know you're excited about this plane, and want to get it done - but Bruce's advice is spot on. Wait and see what Ken does on his, and use that as an example.