|
1. I don't know that this is spelled out anywhere. I would say dinghies and rowboats and such should be treated as Typical Items (DC 10), normal galleys and small sailing boats should be High-Quality Items (DC 15), and anything bigger or more complicated, including all warships, ocean-going vessels, etc., should be treated as Complex or Superior Items (DC 20). Depends on the tech level of the campaign, of course.
2. This is entirely at GM discretion, but this table shows estimated costs for various magical properties. The DC to create a magic item is 5+the caster level, which you can figure out from the spell needed to create the effect you want. You'll need to use some creativity here, and again, GM discretion is paramount.
3. I believe this follows the standard rules for Aid Another, so 4 people can assist, for a max bonus of +8 to a check.