1. There is no limit.
2. It is extremely unlikely that you would have to pay any gift tax, since the lifetime exclusion is $11.4 million.
3. If a gift to an individual is more than $15,000 (2019), you must report it to the IRS on Form 709. HOWEVER, if you are paying his tuition, and you pay it directly to the school, you need not report it. The school must be a "qualifying educational institution". If your gift is for tuition and other expenses such as books, etc., you must report the other expenses if they exceed $15,000. https://www.irs.gov/pub/irs-pdf/f709.pdf
4. From a tax point of view, it doesn't matter, except for the $15K reporting requirement.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
