>>985305On older bikes it's pretty common to find bolts that you'd want different box wrenches for (mostly 8, 9, 10mm, occasional 1/2"). 13mm is rare but I've found 13mm bolts on crappy old bolt-on hubs and seatmasts.
>>985289You're new enough to riding that your thighs burning is likely just the result of using a new muscle, but if discomfort persists I'd get some help with your fit on the bike. Mouth breathing during hard efforts is normal - the only real technique involved in breathing is to make sure you're taking full breaths: focus on using your diaphragm to squeeze as much air out of your lungs as possible, then actively puff out your chest to draw in the greatest possible volume of air with each breath.
>>985238Check that the wheel is properly dished (can be done with improvised tools, see diagram), and if that isn't the cause, check that your frame is properly aligned (google 'Sheldon Brown string alignment test'). If neither of those things is the issue, take it to a shop and ask them to check that your dropouts are aligned (this is not as easy to do without proper tools).
