I think the 1x10" boards will be a lot stronger than smaller ones,though the thinner ones do look a bit more stylish..but function wins over good looks right?..I guess the handles look OK ,but personally,I dont see any need for them,but to each his own..
When driving my MTD I need one hand on the steering wheel (both would be better!) and one on the shifter on the fender for the hydro,(which I think is a pain,I'm NOT left handed and the shifter is on the left fender..a foot pedal would be much prefereable!)..so both of my hands are too busy to be holding any grab handles..
I made some taller sides for a tow cart I had out of old bed frame angle iron,I made a frame out of it,welded it together, and used 3/8" plywood to box it in..very sturdy,but the bummer is if you want to remove it,it comes off in one 3 sided "unitized" peice ,thats very heavy and combersome to remove alone!..it was a mother to drill the holes in that bed frame angle iron too,I burnt up at least 4 new drill bits,and I ended up blowing holes in it with my arc welder instead for the bolts,that stuff is hard as glass in spots!..
I also made another different set of sides later on,that can be removed individually..being ever frugal,I opted to use some free pallets I got for firewood,but decided the red oak 1x4s four feet long were too nice to just burn,they had no knots, and were nice and straight..those sides were pretty heavy too though,good thing they came apart in 3 peices..I did use angle iron on the inner corners ,bolted to the side panels, and pinned to the front panel,to keep them from bowing outward once the cart was loaded with logs
..I've made a lot of stuff from pallets,including the woodshed I keep the firewood in!..cant beat FREE wood,even if it is a lot of labor taking them apart carefully enough to salvage it for re-use..