Did Hitler kind of invite the 7/20 thing by having so many people at his meetings?

Answer 1

Even though there were a number of assassination attempts on Hitler's life, opportunities were extremely limited. 7/20 became possible because Stauffenberg was on staff as a low level attendee. Several higher level officers would have been required at the briefing. Hitler was the target ... all other casualties were collateral damage.

Answer 2

If there hadn't been a need for them to attend, they would not have been invited.

Answer 3

No, that's a fairly standard number of people to have at an important briefing.

And by the way - in Germany and the rest of the world, with the exception of the USA, it would be called 20/7, the 20th of July.  We put dates in a logical order!