Can we confine the conflict to that theater?
No, the first casualty will be the Presidents base.
Depends. Tit for tat doesn’t have to escalate that far if tits and tats are relatively equivalent to each other, but someone has has to be the one to stop at some point or the escalation will grow.
Problem we have is, if we let Assad (and Russia obviously at this point, or they would be so hardline on it) get away with using chemical weapons without a response, it will happen again and/or more frequently
Here's the put up so far:
Russia says they will shoot down any missiles, that's the S-400 and earlier systems and PROBABLY will include Aircraft carrying missiles.
Syria Says Russia will destroy launch Assets, and so far Russia has not disavowed their support for this, that's the P-800 Yakhont and Russian sub & supersonic cruise missiles and Russian Aircraft (all Thermonuclear capable), to strike "coalition" bases, ships, submarines and aircraft.
The US, UK and France has said they will strike Syrian Military bases.
So now someone needs to call, and when they do, we may need a bigger table.
“Can we confine the conflict to that theater?”
That’s impossible.
Somebody will take losses and seek revenge, or to prevent strategic advantage.
If Russia and US forces engage directly, it inexorably goes nuke. And strategic.