Payment forms - Jotform then I reference & manually add the new clients into my Excel file.
Client management - I use Excel for mine (and in the file includes name,email,phone, campaign name, date ordered, requests).
Reporting - Reporb for creating backlink reports for clients.
Keyword Rankings - Scrapebox + their Rank tracker plugin & looking into Serpbook for clients.
But I personally have a hard time scaling it hard due to the amount of "non-automated" work this involves.
How about you & your SEO business on managing your SEO clients?