Hi,
Hope this helps...
1 - I don't model at 1:1, I do it to scale, google sketchup can't work to very very small measurements, so a lot of detail can be lost when scaling down, but is possible.
2 - I always print in sections, it is better to break things down to avoid using supports, the finish over a section of supports isn't as good as you may think - personally I don't worry too much about wasting plastic as its pretty cheap. I find it easier to print one item at a time, I don't nest. Think of a 5 hour print, you check it in the first hour and all is good, so you come back at hour 4 and a part has gone wrong, the extruder has slipped and isn't pulling plastic etc. you potentially have wasted 4 hours and maybe all the parts that were okay in hour 1! Also easier to design without nesting. *this is just my opinion, some people do it very successfully but I'm not a fan myself!*
3 - Shapeways springs to mind but thingiverse is worth a look
4 - I'd buy the printer, make some basic things, ie. a test octopus and a benchy - this tests the set up of the printer, it will be a learning curve with the printer and I wouldn't expect to start making parts ready for a boat straight away, it takes time to get it set up and be able to design the parts so it is printable and repeatable,
5 - I use ca glue ad p38 body filler and it works fine on PLA, All my parts are designed with 3mm tubes in them where a joint is necessary and I used 3mm PLA filament as pins to hold it all in alignment.
Hopefully that helps, it isn't as bad as you think it is, but there is a lot of learning to do!