This is a very popular question, first off, here the dimensions of some riders who have successfully ridden 125GP bikes. 6'3" and 150lbs. 5'11" and 175lbs. 6' and 180lbs. The 125GP engineers probably didn't have you in mind when they designed the bike. So if you like fried food and twinkies, the stock suspension will need to be stiffened up for your big-boned self. Getting a extended/big boy tail can help give you some room to move around the bike and be more comfortable. Longer rearsets are also available from aftermarket manufacturers. John Hjelm is/was making 3cm and 6cm longer rearsets that have gotten great reviews.
Unfortunately they're no longer produced. The classifieds section of this site, Facebook marketplace, or your countries classifieds is a good place to start. Or import one from Japan
If you can legally run Avgas many people successfully run all bikes using that. If you want/need to run unleaded, there are now Avgas replacement racing fuels developed for two stroke machines such as VP Roo99 and CR99.
Wind it up to 10,000 and slip the clutch till you think you have slipped it enough and then slip it some more.
My opinion is that Dunlops are superior to any other tire out right now, they are slightly different now to cope for the moto3's. Many people swear by bridgestones.