And we're off! (Needs to be said at the start of any large project or event.
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It is admirable to see that you have fully committed to this endeavor. Just remember that this is a pretty big project that might stretch out over a modest (or longer) period of time; so my comment is to also consider the "just in time" approach to material sourcing. Some items will have a shelf life and are better if procured shortly before needed (like you did buying just 1 gallon of glue instead of 5 gal pail or buying 3 or 4 gallons at a time... BTW, you might also want to pick up one of the smaller pint size bottles to use/reuse as a refillable dispenser). Also, it can be helpful to have certain things (windows, latches, hinges, etc.) in advance to confirm fits.
On the other hand, things change. Sometimes things just don't go as planned and adjustments have to be made, or creative juices flow and we change our minds as we get further into a project. So my caution is to be careful how far down the buying path you go before the build catches up to the time you need "stuff". Too many people go out and buy their "kit" of stuff and then find that they either can't use some pretty big dollar items when they finally get to that point, or they learn a better way and change their mind, etc. It can really add to the project cost.
It is a juggling act, designing and building these things. They're like one of those parlor puzzles that seem impossible to take apart and/or put back together. You have to be thinking 6 steps ahead and 3 behind all of the time so that you don't build yourself into a corner or waste money on stuff you can't use or overbought on.
On the other hand, there is something to be said for not having to make a million and one trips to the big box store!
Anyway, I guess this is one of those kind of vague suggestions that doesn't really offer a solution to any particular problem, just sharing some of my thoughts as I was working thru that portion of my build.
Examples:
1) Windows - I did a pretty extensive 3D CAD model of my design before I ever started to build... which I realize is not for everyone, but is a really good way to work out a lot of conflicting issues, and ensure parts fitment and compatibility... but you can't always find manufacture's spec.'s online. Case in point, windows. I knew I would be building my own doors and wanted windows with rounded corners, so I needed to know what the corner radii would be. No specs and would likely vary by manufacturer, availability, etc. So I shopped for windows and committed to them right up front. The very first thing I bought for my build. I knew I needed them, knew that I liked the style and quality, and the cost was reasonable. They would be sure to fit because I would be (did) building around them.
2) Foam - Having the model I had a pretty good idea of how much 1-1/2 and 3/4 inch foam I would need for the whole project, and since the 3/4 inch stuff had to be ordered I wanted to be sure to get that sorted all in one go. It was a pretty good stack of foam when you added it all up, so buying it from a commercial lumber yard and the fact that they offered free delivery on that level of purchase just made sense to buy it all up front. <edit> I did end up with a bit left over, which I figure was due to the ability to piece your drops back together quite easily, so despite having a decent pile of chunky drops and scrap, the yield turned out better than expected. </edit>
3) Plywood - More specifically, 5mm marine grade Okoume. It was relatively expensive by the sheet (about $65), but I knew I wanted the quality, it had to be ordered from Canada, and there would be a pretty hefty crating/truck freight charge, so I needed to order enough, but didn't want to overdo it. I used a free cut list optimizer (found online) to nest all of the parts from my model. The program allows for the saw kerf and lets you specify the direction of the grain when/if it matters to you. The first couple of times thru the program I was pretty appalled at the amount of drops/waste and how many sheets I would have to buy, so I broke up the panels for my floor assembly and bulkhead wall skins into smaller parts to take advantage of some of the would be drop. I was able to reduce the sheet count by 2 or 3; it meant more work for me adding some framing to back up the joints and getting nice clean butts (messed around trying to do scarf joints but gave up before achieving the quality I was looking for)... and there were some pretty white knuckle moments as I was getting down to the last few larger pieces... at which time the cost of having to buy an extra sheet upfront paled in comparison to the nervousness of potentially running out and having to pay the shipping/crating fee again. In the end everything worked out and I still have a bunch of remnants to make lantern boxes and galley compartments, etc.
4) Epoxy (glues, paints, etc.) - Has a shelf life and is sensitive to climate change; can't be stored in freezing temperatures (like my work shop with limited heat source). I only buy enough to see me thru the foreseeable stages at hand, maybe a gallon at a time.
Okay, well, I have rambled on enough, but I just wanted to give a little 'food for thought'.