Most brands should work fine. Same with hairspray.

I've been using glass print surfaces and glue stick for 10+ years. I just wash off the glass with warm water every 2-3 prints otherwise just add a new layer of glue stick before printing. I'm going to try a G10 print surface next as I finally found some in my country.

Any brand will work. I dont like glue, but its easy to apply and also clean it with water. Glue can fix huge problems like uneven bed, wrong temp etc. You are facing common 3D printing problems. Not sticking to the bed and curling. It can be frustrating, get some patience and you will sort it out.

You did major upgrades, so tunning is hard to avoid. Do PID tuning for your hotend, your temps might be not stable. Check your hotend mount for play. Make sure your part cooling fan is off on the first layer. More squish, higher temp and low speed are your friends. Try with 205/60 C and 10-15 mm/s. Check your retraction, you might have oozing that can cause not sticking at first. If you are printing tiny parts like 5 mm circles on first layer you need to have crazy dialed printer to print that consistently. Still possible of course, but even then some issues at start /end of extrusion can occur. 0.24 mm first layer height is much easier to print than 0.15, simmilar thing with nozzle size. Your filament might be shit, better filaments are more forgiving.

Print 1 layer square and take a picture. Lines must fuse and surface shouldnt be rough when touching it. If you didnt print 100 squares dont give up yet 😉

Edit: any PVA glue stick (the one that is used by kids in school to glue paper)