Is it best to check in online or once you arrive.
Online check-in gets your paperwork and key printed up ahead of time, and you stand in a separate line which may or may not be shorter than the regular check-in line. You go up to the desk, show photo ID, they hand you your key and packet, and you're on your way. If you think you'll have a lot of questions for the front desk CM, or might want to change your room location at check-in, online check-in likely won't save you much time, and you might as well check in when you get there.
I keep seeing folks asking about room requests, is there anything I should be requesting at SSR (we are early 40's sans kids).
Some people have strong preferences for particular locations, views, etc. If there's a particular area you'd like to be in, or a particular view that you want, by all means call MS and make the request. If not, there's no need to make requests.
Can you pre-pay baggage for return flight like you do when staying on a nonDVC package?
Yes. DME and the return flight check-in are exactly the same as they are at all Disney resorts.
Is it ok to order tickets from Mouse Savers.
Yup, you can buy your tickets any way you like. There are no packages with DVC, so there's no ticket purchase requirement.
Will purchases be sent to resort like nonDVC stay?
Yes. DVC resorts are Disney resorts, and the resort operations are the same. DME, package delivery, transportation, free parking at theme parks....all the perks of staying at a Disney resort are the same, regardless of whether you're paying with cash or DVC points.
The only difference you'll notice is that you won't have daily housekeeping included with your stay. Everything else will be just the same as your other Disney resort stays.