Great concerto, I love the viola, and this piece is exciting as I think you're a viola player.
First mov
Good intro, in the romantic style. Pertinent accentuations as when the celli and counterbasses become a bit active. There are many cadenzas or quasi (with little background, as a recitative which brings a very tranquil mood. although it makes the movement a bit long to my taste.
I see you are using slurs for expression in the strings. Some people discouraged me to do it. What do you think? I've read that Brahms sometimes wrote double slurs, one for expression, the other to establish the phrasing. I usually put a "legato" indication (I see you do it sometimes, too). In my opinion, whenever it is clear to understand it... it's OK.
I find the Andente more coherent, perhaps with some motives quite romantic. I observe some ppp dynamics in the winds. Mr. Alan Belkin advices, in general, to stay between pp and ff for all the orchestra but timpani (within can do fff) and strings (which can play ppp and fff). The piano is different and can do also the whole range.
The Finale is a nice contrast to the slower movements.