Here's what I did with one of mine (actually two). https://www.mopedarmy.com/forums/discuss/read.php?f=1&i=461041&t=461040
5-10 up hill is not normal, but no offense 280lbs is not normal for a moped either.
I weigh in at about 180 and with 14-45 gearing on the above mentioned bike I can pull 25 up some seriously steep hills/mountains (6%+ grades), I took it up to 9000' above sea level last week without a problem. It can still cruise at 30 all day and tops out downhill (and screaming) at about 38.
Really what you do to the bike as far performance parts go is all up to what you want the bike to do. Do you want a good all around daily driver, do you want a top-speed flat land screamer, do want a torquey hill climber, etc., etc.?