lots to consider all right.
boat lenght certainly is important but unfortunately it is important only to you! I was thrilled and happy with a 16 ft Wayfarer for years. Now a 34 seems about right. My charter experience leans me to over 30 feet and sailing shorthanded about 32 feet. there is room below and the deck is short enough for a scamper to untangle something but long enough to stow things on and to get rid of that corky ride you get in little sailboats.
Things I have come to appreciate are a tiller or auto pilot, GPS, radar, and a good Antenna (yes, antenna and connections) on a modern VHF which has the digital selective code and panic button. Charts that never see the cockpit: nav table only--so they stay good and don't go overboard. I also have come to appreciate blown out lines, whether they are from the head or galley or related to engine cooling, and a simple steering rig, I like tillers.
The boat has to be able to lock down in a blow, and that means the rigging as well as your dinghy. The lockers belowdecks esp. under the salon seats need wingnuts on them to prevent them dumping in wild water. Somehow you have to be able to hotbunk in the aft cabin because if you get into it the veeberth is good for stowage and little more. Someone who can turn out decent food without chundering is valuable on a long trip.
As for personnel, you need folks that can look, see, and do. You are going to be exhausted if you are constantly consulted on sail trim and navigation. Also a sense of teamwork, with a little forgiveness for screwing up, which you will all take turns at.
I prioritize as follows: firstly it's the wind and water you are in... then the size and condition of the boat and its rigging for that water. Then it is about the crew and their physical/mental shape and experience. Finally it is about the safety of the passengers. Put these in any other priority and you are going to have a tale to tell.