The mansion tax is the buyer's and starts at 1% of the whole price at $1m, stepping up from there. If you finance, mortgage recording tax adds roughly another two points. On a sponsor sale the buyer often absorbs the transfer tax as well.
Closings run through attorneys and a title company, not a notaire. Title insurance, not a public register's guarantee, is what protects you — and it is bought once, at closing.
No Social Security number is required to take title. FIRPTA withholding hits foreign sellers, not buyers, so it is an exit problem to plan for rather than an entry barrier.