I think Rouge One is the perfect movie to start off with the side movies as you can have the face of star wars in it with Darth Vader. With James Earl Jones coming back to voice him it's no surprise why they picked that one. I do think Han Solo is the most iffy of the side movies because he is so iconic with Harrison Ford playing him. But Lawrence Kasdan is helping write it so hopefully it doesn't suck. I think a Bobba Fett movie showing what all he did between 3 and leading up to 5 would be good with possibly the end of the movie showing him getting out of the sarlac pit if they decide to keep him alive.