The PP is talking about WDW so most of what she said is not relevant to DLR/DCA.
I would go for the 4-day hopper pass. It's not that much of a price difference between the 3 and 4 day hopper if you are only doing Disney on this trip.
You are going during the Christmas holiday, when all but two passes (Signature Plus and Premiere) are blocked out so the lines shouldn't be as bad, but they will still be bad. As soon as you get into either park, you should get the Max Pass, which is a digital fast pass. It is $10 per ticket per day so get it on the first day and get there when park opens. This saves you time to run all the way to one end of the park for a fast pass. Plus, you can get a FP for the other park (DCA) when you are in DL and vice versa.
Here is a recent review of the Max Pass:
https://www.disboards.com/threads/just-back-max-pass-is-totally-worth-the-cost.3649453/
Christmas Day is a nice day to go; it doesn't get busy until later on in the day since most people are at home spending it with their families. Remember, you don't have to go 3 or 4 consecutive days. You can take a break in between. You just have to use it within 14 days of the first day that you used the ticket.
How often have you been to either DLR or WDW? That would help with planning as far as "must do" rides versus others. You should definitely partake in Indiana Jones, Buzz Lightyear, IASW, and Haunted Mansion Holiday (the last two due to the holiday overlay that isn't available at WDW)