Most likely that would be 10mm or roughly 3/8" thick glass ,1" glass is rare and for aquariums 25x your size , that tiny chip should be fine from what the pic tells but like most things in life there's never a guarantee
Oh and yes level stand not the tank , the tank is only as level as the stand which is only as level as the floor and so forth , floors are often off level over time
Welcome and keep us updated with pics