Killing my own onboarding bottleneck before it eats the retainer

I run a paid newsletter for independent consultants and I just moved three of them onto monthly retainers, which is the first time recurring revenue has actually been real for me. Problem is every new retainer still gets onboarded by me, over two calls plus a spreadsheet, and I can't scale past four without drowning. Writing this down because I keep telling other people to systemise and then not doing it myself.