最好还是找个律师搞定

需要哪些手续和文件？

根据我有限的知识，至少要以下文件：

Assignment of XX% (the percentage you will get) ownership interest from XXX (your friend) to XXX (you) (date of execution)

Bill of Sale of XX% ownership interest from XXX (your friend) to XXX (you) (date of sale)

Buy/Sell Agreement (agreement effective date) - this is to protect you both

Consent to Transfer of Membership Interests to XXX (date)

Amended Company Agreement (approval date) - this is to document the membership change

Employment Agreement with XXX (your friend)

Employment Agreement with XXX (you)

Membership Certificates

我的建议是，朋友归朋友，business is business。还是找个律师来弄好应该有的文件，以避免将来不必要的法律和利益纠纷。Hope this helps and good luck to y'all! :)