Steps to remove Ultegra and install SRAM Force disc brakes with internally routed hose
Your steps are all correct, I suppose the main issue is how not to spill brake fluid everywhere and how to route housing internally without any frustration. I've been through the same recently and know how annoying the job can be. Apart from draining the system, you have several options:


Use a special barb that threads into the hose and has a hole to attach the thread to. The "RockShox Reverb Stealth Barb Connector" can be found on eBay for 10USD. There are other similar products too.
Source about two meters of ~5mm 2:1 heat shrink tube and connect it to the old housing before pulling back. You can cover the open end of hose with a piece of plastic bag, the heat shrink should hold it tight enough. Repeat in reverse when routing the new hose. I did this with shifting housing and see no reason why this approach wouldn't work with a hydraulic hose.