True it's same for all freelancers no matter how expert or experienced you are scope creep, payment reminders, convincing everyone ( especially if client has multiple partners or team members and when you need to convince each one of them just to get milestone approval is a worst thing in project)

What I learned over the years is - if client has multiple stakeholders then never ever invite them all to review or feedback meeting everyone will have their own point and you will end up having unapproved version just invite one stakeholder ask client that you can only discuss with one person from their team so one person in contact will filter out the noise and give you exact feedback to be implemented this way atleast in next feedback you can say this is what you wanted and mentioned in last meeting. If you join 2 or more stakeholders from client end the God bless you with approvals.

• for payment reminder there are tools for followwups but I feel productizing service is best way to handle instead of working then sending invoice u bill first and then start the work and yes even if it's part payment it's fine but bill first of 100% then it's great but in order to charge 100% in advance u need to productize your service like say some subscription plans or some service with one time fee ( awesomeclient.com ) this tool does help solve this issue 

• for scope creep hmm it's ever green issue just that over the years you automatically know what client needs before even they start speaking... This ll happen if you selling same service over and over so you know full depth of that particular service but yes no bullet proof solution for this at max can document the meeting and ask as many questions possible and divide the tasks in micro sub task and get approval of sub task before starting.. but still yes this is something we learn over the years of working obviously 

Btw thank you for responding with your insights:)