You absolutely can use your own router and should be able to use your own modem as well. They should have a list of approved modems on their site and you can use whatever router you want.
If you're looking for a Sim City clone, I've always been told that Cities: Skylines is the way to go. I picked it up in a sale years ago and need to get around to trying it sometime.
The best you could probably do would be to uninstall the crapware that you can, disable what can't be uninstalled, then install a launcher like Nova. Otherwise it's root and rom.
Spent $5 for the 30 day gems, at AR 32 now and interest is fading fast. Fucking around exploring the world is the main draw for me. With things not respawning or changing in some way I'll likely stop playing once I get all my gems from the pass.