Great first project that tries a lot of things.
The two critical dimensions you’ll need to worry about are the threaded parts. The rest can be off and not seriously impact usability. You’ll need to establish the tolerance limits for the hole to be tapped/threaded … then the major diameter of the cap portion to be threaded.
I’ll give you my piece of rod so you can practice this several times - this is going to be your critical features. Boring the right diameter hole shouldn’t be a challenge. What I would suggest is you make sure you have the right drill size, the right tap to do it, and then the matching die for threading the cap. You may have to tweak your design to match the tools you have available.
You’ll need to research what the limits of the major and minor diameter of threads are so you’ll know how much you can be off in one direction and compensate in the other (It’s not much). Practice doing this successfully a couple times before doing any of the other work. When you’ve done that, the rest is easy peasy with lots of slop tolerance that will still make it functional.
I have a Orange Bin in the Galley, middle height, in the middle section along back wall. Labeled David Kessinger. The rod is in there. Feel free to go get and practice doing the threads before anything else - and have at it. Threading isn’t that difficult - but things have to be cut straight, threaded straight and within limits.
RE: Dimensions. You need to dimension what the hole size is for the threaded hole. You are referencing off the outer walls - the hole size for the tap is critical unless the .26" bore diameter is the minor pitch diameter (i.e. the size hole that will be tapped. That needs to be dimension to .XXX" -.000" + .010" would be my recommendation. If undersized too much will be hard to tap and may break the tap. You’ll need to dimension the .3" dimension to .XXX" +.000" ~ -.010" (or .015") not perfect for threading but workable - assuming they aren’t at the limits going the wrong way. E.g. small hole large cap, large cap, small hole.
I know people get annoyed with me because I always ask “What’s the tolerance?”
Using this chart your .3" dimension could be .1"~.5" (.4" range) - not acceptable. If .30" then it can .29" ~ .31" a range of .02’ that would be the absolute limits, IMO (but it also means if the hole were at the small end it would be .1", if the cap at max diameter it would .27", this equals .17" or a little over 5/32" which is more than the threads and half the size of the hole), notice the ranges I gave above are TOTAL ranges that would equal ±.005" if the nominal size is centered on the dimension.
Hope I haven’t confused. But the make or break features are the threading. Master that first.