For example, the Rikers Island jail is mostly for pre-trial detention. People don't get sentenced to Rikers.
No, he's been in jail. Semantic, and a bit simplified, but basically you're held in jail pending trial, and go to prison for a conviction.
Days spent in jail are counted for your “prison time” so it counts as such even if it is jail ;)
You can't be told anything irl, can you?
That may be better directed at that comment's predecessor.
Federal prison will be a step up from the Metropolitan Detention Center. Here's a guide to the best Federal prisons.[1] Since he will probably be serving more than 10 years, he's not eligible for the "Club Fed" minimum-security federal prisons. Low-security, probably. He's not violent or an escape risk.