Apps: this site uses Webflow for CMS, Memberstack for memberships, Stripe for payments, Stripe for order confirmation emails, and Mailerlite for email updates. Research can be done on each app to determine whether it's within your accepted levels of safety
Personal data: payment information is encrypted on Stripe (site manager cannot access it); other personal data involved is your email address & password. your email address is stored in Stripe & Mailerlite, and your site password is encrypted in Memberstack (site manager cannot access it).
Account deletion: upon request, your account can be wiped from Memberstack & Mailerlite