I really don't think you should bother with AR10.3 at your current rank.
However... if you really want to learn it (I mean this is a game, its for fun so, why not?) just edit songs you can play well on AR8+DT to AR9 and try it out. Honestly though I think its best if you try to learnt he AR's between 8 and 9.
Personally I started playing a bunch of 8.5+DT, then 8.7+DT and made that final leap to 9+DT.
However... if you really want to learn it (I mean this is a game, its for fun so, why not?) just edit songs you can play well on AR8+DT to AR9 and try it out. Honestly though I think its best if you try to learnt he AR's between 8 and 9.
Personally I started playing a bunch of 8.5+DT, then 8.7+DT and made that final leap to 9+DT.