These are the sonatas you should DEFINITELY investigate-
No. 46 in E Major, Hob. XVI/31
No. 47 in B Minor, Hob. XVI/32
No. 48 in C Major, Hob. XVI/35
No. 49 in C sharp Minor, Hob. XVI/36
No. 50 in D Major Hob XVI/37
No. 53 in E Minor, Hob.XVI/34
No. 58 in C Major, Hob. XVI/48
No. 59 in E-flat Major, Hob XVI/49
No. 60 in C Major, Hob. XVI/50
No. 62 in E flat Major, Hob. XVI/52
I can't speak enough of No. 50, 53, 59, 60 and 62!!!
Also check out the F Minor Variations and the D Major Concerto, they are great!
My favorite work by Schumann is undoubtedly the Symphonic Etudes. Listen to Richter or Myra Hess for these. Also worth looking at- Kinderszenen, Kreisleriana, Waldszenen, Opus 17 Fantasy, Carnaval, Abegg-Variations and his piano concerto