Made the trip two weeks ago. The trip over depends on the day. Sometimes its six foot seas, sometimes dead calm. We have encountered fog and do not have radar. I am not sure how you are as far as fog goes, but people have been traveling for many years in fog without radar. be sure to check the forcast for LI sound as well as Block Island sound. You can check here.
http://www.wunderground.com/MAR/AN/330.htmlSometimes you can run to the outside of Fishers Island, sometimes you should run inside. The later is usually more comfy. The run for us from Mystic is about 15-17 miles. It takes us about 1 hour 15 minutes from the Brewers yard in Mystic to the pond in Block. The last time we ran there it was about 3 footers there and about 2 coming back. Be mind full of the tides as well as the winds. If its too windy it will be choppy, not enough wind, usually = fog. Have a back up plan in case it gets crappy.
As far as marinas go, if you want quiet, call the Boat Basin. Always a private slip. We usually do the hook, but you can also get a mooring.
The most important thing to remember about the trip to Block is, Most will say its very hard to get to with out radar, take it slow and easy, dont rush and have a great time.