Yes meet with Solicitor when Donor has lost capacity. One of the first steps is serving the Notice of Intention on the Donor, Notice Party's and Wards of Court Office. Then you wait 5 weeks before you can service the Application for Registration (aka Form 1). The Form 1 must be served by personal service on the Donor. As far as I know,in terms of the 5 weeks, they look at the time between served dates. I think it's to give time if someone wishes to object? But I'm not 100% on that one.
In terms of the Medical Cert, after you send the Notice of Intention, the Wards of court office will post out a checklist of docs and Practice Directions for the Medical report. You would be better off waiting for that as they can be strict about what's in the report - if it doesn't meet the requirements they'll sent it back and request a new one be done. Don't get caught out like I did - got the medical report done before we got the Practice Direction and it wasn't detailed enough so we had to get a new one!