CBIR
I'm currently using EFT who have Diamond aircraft/simulators.
I did my SE CBIR with them. 25 hours sim & 15 hours in the DA40 with a first time pass ( this is credit to the usefulness of the sim and the great instructors at Euro Flight ).
My initial plan was the same as you, an IR(R) first followed by hour building then CBIR route with hours credited. However due to full time work I elected to start the full 40 hour SE CBIR with zero IFR experience, so please ignore schools that say you can't undertake a CBIR course without prior IFR experience. I work full time so valued the 25 hours in the sim which isn't affected by weather, and allows you to carry out 4/5 approaches per one hour session versus an hour in the air where Bournemouth may keep you in the hold for 30 minutes whilst Bryanair jump the queue, leaving time for one approach. On the flip side of this, sim time doesn't count as flying time ( thinking 200 hour flying requirement for cpl skills test ) so you'll have to budget for 25 hours extra flying elsewhere...cheap tomahawk for me at my local field at the cost of £2500. (25 hours IR flying in the DA40 would have cost me about £7500)
And then to answer your question, the SE to ME IR upgrade at EFT and as per the CAA requirements is minimum 3 hours sim (DA42) and 2 hours in the aircraft (DA42). I'll be doing this after my MEP training ( 6 hours ) and CPL training ( 5 hours in the DA42 after 10 hours in the C172 ) so I'll be more familiar with the aircraft.
Additionally I used a DA40 aircraft on Flight Sim 2020 to practice approaches, checklist flow and use of the G1000 which was invaluable. There is now also a new DA42 available on Flight Sim by a developer called COWS who consist of flight instructors and students that is fantastic for at home training and brush up.
By doing the 40 hour SE CBIR then an upgrade to ME CBIR I save myself around £6k total versus doing the full 45 hour ME CBIR. Although you may value the consistency of a full course on the multi aircraft.