May be a stupid question but what are the benefits of online check in? Don't I still need to visit the counter at arrival so I know what room we have? And yes, we are using Magical express and Disney transportation. Starting to think it's nearly impossible to try to get to Epcot that night...
It's going to be stressful but it's possible.
Even if you don't get your room number via text if you do online check in you could theoretically go straight to Epcot upon arrival to your resort.
You would get on ME, go to resort, drop any bags you don't need with bell services and then call for Uber/Lyft or get on a Bus, depending on time of arrival and FP.
Then when you are ready to leave Epcot hop on the monorail then get on the MK monorail and then get the boat from MK to FW. This is probably better than the FW Bus from Epcot since the boat brings you out right at the HDDR location.
You do stand a lot better chance of going to Epcot first than you do going to Epcot after HDDR
If you want to try, book your FP for something like 3:30, 3:45 or 4:00. Ride TT. If you have time, do more, if you don't, go straight back out to head to HDDR. It would be rushing around but it is possible. Depends how much much you want to skip rope drop. If it were my family, I'd book the early FP, hope to make it. If I don't, I don't, I go straight to HDDR and plan RD later in the trip. If I make it, great. One less early morning.
And all that said, you stand a better chance of getting to Epcot after HDDR than you do seeing RoL in January.