If the weather is ever bad enough to need harnesses, I've always rigged jacklines attached to cleats or solid attachment points. I've seen ppl use harnesses in flat calm weather, or not until going on deck in 40knot winds. YMMV depending on comfort level, but I'd never trust a lifeline to hold me onboard. Stanchions are fine too, but mobility is a bit restricted that way IMHO. Actually I'm wary of using the lifelines to hold onto when moving around using "one hand for the ship" too, but that's probably a comment on the quality of my lifelines!

I used to laugh about practicing MOB, too, but there's going to come a time when you were glad you did it. I remember trying out our lifesling one day on a lark, and then ended up using it 2 days later to rescue a badly injured person in a dangerous situation. Sunbvi's comment about not needing MOB is, I think, losing something in translation since his IP address is from Germany.

IMHO at least 2 ppl on board should at least know how to start/stop the engine, steer the boat, and have some idea how to drop the sails just in case of emergency.

Everyone's going to have their own opinion about outside captains based on their own comfort level, but I'd do it if you or your partner is even slightly nervous. Being nervous or scared is no way to go through your vacation. Also, anywhere you can get to on your first day will be no problem for your captain to wangle a ride home from.