1. He missed the # 7 bus.

2. He missed Bus # 7.
3. he missed the Number 7 Bus.
4. He missed Number seven bus.
5. Hhe missed Bus Number 7.
(Which ones are correct?)

I assume that this is one of several buses that travel Route Number 7.

If so, then 1 and 3 are correct.

Numbers 2 and 5 are correct if there is only one bus number 7.