Honestly doesn't matter what order you play the routes in, but personally i would put TJ last cause its like the most chill out of every route and you might get the wrong idea of the game if you just play his route and nothing else. I would put Leo first cause its like the go2 route to go and it captures echo well. After that it doesn't really matter which ones you play. I would go for route 65 after echo so you have some more background wich is nice, i think it would have felt out of place not having the knowledge of route 65 in one route specifically. (Route 65 is also pretty short and all routes there are more or less the same so you can go through it quite quickly)
Tsm i would read after Echo and route 65, cause it fills the gaps nicely which you will have after Echo.
About arches idk, haven't played it yet but will do soon!