Can a non-US citizen file a provisional patent in US? Does he need to hire an attorney or can he do it himself?
What does he need to do to convert the provisional patent into a final patent? (meaning: will he need an attorney?)
In Short You dont need a attorney if you are inventor of invention. All patent offices can deal with the inventor/applicant itself. Its the local address requirement which makes it harder or to require attorney (because of confidentiality). However for filing you can follow my earlier answer here Patent filing procedure without a patent attorney
Some relevant excerpts are:-
what if inventor or applicant is not from the USA?
Most of the countries prohibit direct filing of patent application to foreign countries. These are called security restriction. It depends on your resident country. TO better evaluate situation inventor has to check respective country ACT and Rules before filing a patent application in foreign country. PCT has listed respective sections of some countries -- following link
How to file a patent with the USPTO without a patent attorney?
You can file patent application using EFS-WEB provided you are inventor of invention.
Can be a patent filed online?
YES USPTO application can be filed online at EFS-WEB
Where can I get detailed information about the procedures and fees?