1. There is EveryPay https://every-pay.com/ . You need to open an account in the LHV bank first before receiving payments. (disclaimer: me and our dev team built their tech platform)

2. All the EU data laws apply.

3. I guess it depends on how you specify it in your contracts, you could do the disputes/arbitration wherever you want. There is an overview of dispute options here: https://www.eesti.ee/en/entrepreneur/legal-aid/resolution-of... . For example, if you have a customer not paying their invoices that are below 6400 euro you could file an a request in E-toimik/E-file (a paperless court system) and the collection is automatic. You could also sue people "online" there. (disclaimer again, I lead the software architecture/development work on the E-file project.)