Bandesaws: I posted an article on 14" bandsaws and their price/value. You'll find it here
. However, it might behoove you to use your table saw instead. Build up the height of your fence. Make sure you have feather boards supporting your work and keeping it in place. My consideration is that it is easier and faster to push through 20' of wood twice rather than trying to keep it on the straight and narrow using a resaw fence. Even cut in 8' lengths resawing needs muscle and concentration and it ain't fast. Are your 2x4s 2"x4" (that is to say 8/4 x 16/4) or are they milled down. Usually gifts like that are rough sawn and when the donor finds out hemlock is toxic they give it away. Our local saw mills are pretty wary of the stuff. The wood itself is fine, it's the dust that kills.
Dust Collection: Your Hemlock is dangerous and toxic. It is also a carcinogen. Do not mill it indoors. Even outdoors make sure you use goggles and breathing mask. It is the quintessential medieval poison.
Lengths: I would leave the lengths at 20', jig up good-sized infeed and outfeed tables and stout feather boards to keep the work tight to your fence and "have at 'er".
Back side relief: I concur with Dan. Make sure you're putting reliefs on the backside. It will help keep the finished product from warping. Especially where you are, heat will move from none to damned warm. I heat with wood and my temperature varies in the house (I have brick veneer) from cool to damned hot, especially early in the season when you only fire once a day.
Router: I can't agree with Mike on the router. I'd want as much meat behind the bit as possible. Get a good 3 1/4 HP Makita or Hitachi. Now, they are both excellent workhorses but the difference is that the Hitachi is already modified for cabinet bits whereas the Makita might not be modifiable. I would suggest that you get two of them, one each of the Makita and Hitachi. I don't like the new Hitachi M12V2 so if you can find an old M12V I like it better. The Makita 3612C is a nice machine but not as versatile. Huge bits become a problem with it -- the base requires too much modification.
You're going to have to build yourself a router table. Unfortunately, OakPark has gone out of business so getting functional baseplates could be a problem. I would suggest that you make your own. They're not difficult and there's lots of information on the forum on how to do it. Mike will have the addresses. I'm suggesting you keep your table height around 36" from the ground. Again, you don't want to be doing this indoors. Your milling will require support so I would suggest that you make a milling jig for each stage of your project. Like that you can just push them through. Feather boards will be essential as will long infeed and outfeed tables. I'd use a few of those 2x4s to make your tables.
BTW, I hope you're using PEX for your plumbing. I'd also recommend an inventory of sharkbite connectors for the occasional break. PEX is pretty forgiving when frozen but not indestructible. I'm using a Viega Manablock. Works well but it doesn't like getting frozen either. Our hydro goes out at least once a winter. We're fine, we're always home but if you're in a crisis in your profession and you bring the family into town for a big storm, that's the house without heat and a few burst pipes. The damage comes when the hydro comes on and the pump kicks in to build up the pressure only to fill the basement. In our case it was the barn. One of the doors blew open in the night and the pipes froze. One of the horses was cornered in his stall with water spraying from a broken pipe. You should have seen the look on his face