Dude , one at a time
if you are roaming, mot likely you will have 1x which is much slower than EV. Yes the performance of your TV and others internet app will suck. If your signal is weak that impacts your internet connection, when it is weak and you are on the vere of losing it, you switch to Roaming, make sure it is included in your plan though.
You are right on SMS and emails, you can be talking on the phone and send an sms, but you can not send an email unless you are using wifi.