Question: Soldiers tunic at the time of Trajan

[Peroni]

No boots yet, btw should these be with open or closed toes?

Either pattern is correct. I sometimes wear caligae, but mostly I wear a closed calceus as I find them more comfortable.

I ve seen a picture of Peroni mounted, perhaps he can tell you something first hand of his experience about that.

I have never ridden with a dished shield, only flat. It isn't uncomfortable at all. My cavalry shield has straps fitted to the rear face to assist with support whilst riding. The longest strap goes around the shoulders. They can also be used to sling the shield over the horns of the saddle when dismounted.
http://i20.photobucket.com/albums/b242/ ... CF1830.jpg

For the shield boss, I would go for a round plate, not square. Most depictions show round.