The answer to the 75 mile question is "it depends". If you are beating into the wind the entire way, making no more than 5 knots and having to tack back and forth, you're looking at a 20 hour sail. If, on the other hand, you get lucky like I did when I went from Port Washington, WI to Pentwater, MI (about 75 miles) where I had south winds 15-25 and I was able to simply hold a 75 degree heading the entire way and never saw less than 7 knots, you'll make it in 11 hours. The latter is definitely doable. I wouldn't want to do the former by myself.
As far a thunderstorms go, I'm not sure what the option is besides riding it out. If you are really close to a safe harbor and it is looking really bad, I'll probably do that. However, in most cases you'll likely be a few hours from a harbor and the thunderstorm will likely fly through by then.
"To reach the port of heaven, we must sail sometimes with the wind and sometimes against it - but we must sail, and not drift, nor lie at anchor.”
- Oliver Wendel Holmes