McDonald's is in some technical, economic sense a "restaurant" in that it serves food for pay. In non-technical everyday usage, the word "restaurant" implies table service, excluding places where you must carry your own food around.

It really depends. Where I come from, 'Should we go to a restaurant' is rarely used. We'd usually say 'eating out'. And McDonalds was definitely 'eating out'.

> In non-technical everyday usage, the word "restaurant" implies table service

The english language varies considerably by geographical region, the speaker's socioeconomic class, etc. Your statement is not universally true; I've met people to whom it's true and people to whom it's not.