We built one nearly the same.  I like your walking axles, but on a smaller sprayer may not be necessary.  The wide wheel stance is good too.    We pull ours with a 900 Kabuta too.  I put the tank on the Kabuta though.  I was concerned with tongue weight with it on the sprayer, and traction pulling lit if it was on the sprayer

We are using a Micro-Trak controller now, after using it the first year.  Difficult to hold speed constant using a foot throttle, and sometimes uneven ground, terraces etc