Go to the search bar along the top of the site, type in "front sprocket nut" this will give you all the info you need on a known fault...best done asap.
1st gear is always clunky to engage, totally normal, 1st to 2nd should be done gracefully without revving the nuts off it in 1st then trying to engage 2nd & also trying to be too quick with the change can result in serious crunching.after that the gearbox is sweet & the engine loves to be revved.
Handlebars are soft as chocolate, if it has ever fallen over i reckon the bars will be bent.renthal 758's handlebars are a nice upgrade on standard.a jck up kit comprising of shorter dog bones will improve the turn in on corners.
Apart from that a k&n air filter & decent end can is a nice mod, no need to do any re jetting.if you do an oil change make sure you buy a k&n oil filter as they have a nut on which makes taking it off next time much easier.
Basically a nice bike as standard really so not too much to do.
Oh & welcome to the forum.