I agree with what T20thoughts said on the matchup.
To expand on his first point, once you score a knockdown, Sim has no answers to a meaty divekick/crossup/whatever except to teleport or use EX Yoga Blast (invul startup). You should always be pressuring him after you score a knockdown.
The only thing I would change is if you get a life lead, don’t let up on Dhalsim. Keep up the pressure, don’t give him a chance to get room otherwise he can setup his spacing to chip away or ultra to better effect at range.
My own advice is:
c.MP his j.FP if he uses that. You can sometimes roll under j.FP as well but it’s not always safe (psychic or spacing?)
Another important thing to learn is you need to get your spacing down and get close enough to normal messiah kick over his Yoga Fire. Ideally with enough EX to safe cancel and then proceed with the beatdown.
RH normal Messiah will not connect at his max c.FP distance you need to be slightly closer in order to get a successful hit.
If you have 3 bars and you absolutely have to get into Sim, you can do the EX Tornado, EX cancel trick to make up ground but you’re burning 3 EX for potentially 0 damage.
Finally, keep how much stun you have in mind. Eating a few limbs in a row can definitely build up alot of stun without seeming to lose alot of life. Stop for a moment and lose that stun before going back in. Getting stunned is not death in this matchup, but it will make coming back alot harder.