You will lose quality from rendering, even if the pixel dimensions are unchanged. No free lunch at this diner.

Lets say I have a 1366x768 video that contains inside of part of a video (1280x720) I want to crop to.

If I set the project to be 1280x720 and then crop the outside part myself will I suffer quality loss because the original video file was first resized to.

No.
Because your original video file will never be resized.

The "ideology" of VEGAS goes in a way it compares what it was "fed with" to what it was "requested to deliver" and it does only do the processing required to satisfy the request during render.

Rendering creates losses, period. One cannot simultaneously crop pixels and not render. One cannot smart render with cropping on the timeline. There will be quality losses. That is the information requested by the original poster, without blowing any smoke.

C'mon guys, please..........?

It may not be blowing smoke, but it isn't what the OP was requesting. They wanted to know if resizing will result in additional quality loss, the question had nothing to do with rendering itself.