ET - I'm not an expert but I think your understanding is right.....5 foot wind waves on top of a 7 foot swell. The other piece is swell timing. A big swell with long times between waves isn't necessarily bad.

Hopefully other people can comment, but I've heard anything big (10+ foot swells) with less than ten second timing is getting rough. There are lots of shades of gray though and experience helps.

Regarding forecasts I usually check the NOAA marine forecasts (using the NOAA site) and may check data from any weather buoys near where I am boating.