You haven't mentioned customs duty either which is quite a cost, too.
Can you get items from inside EU and not pay customs (like here in Finland) or do you still have to pay customs even from within EU? If you don't pay customs from EU you can order the Teensy from floris.cc, find a Cherry G80 board from ebay.de or Amazon.co.uk (or a second hand board locally) and then the only "difficult" part is keycaps.
For keycaps you should finalise the layout first and try to use at least standard sizes:
1x, 2x for number row,
1x, 1.5x for "Q" row,
1x, 1.75x, 2.25x for "A" row,
1x, 1.25x, 1.5x, 1.75x, 2.25x, 2.75x, 6.25x, 7x for "Z" row and bottom row
Unless you're okay with using a "flat" profile like DSA, in which case you can use any of the standard sizes on any row.
First off the next few paragraphs are my personal opinion and I'm sure there will be people who disagree. I do not mean to be critical of your layout designs, as I'm sure they are all at least a partial improvement in terms of efficiency over the normal horizontal stagger QWERTY layouts.
In terms of ergonomics, split and vertically staggered is best for the finger area, but that requires 2 plates and really changes the whole design paradigm. I'm not a fan of matrix or symmentric stagger layouts as I see very little advantage over "normal" horizontal stagger with the way I type (floating and moving the hands over the board) and the familiarity of the normal layout takes precedence for me, unless the ergonomics are vastly better.
IMHO, anything "between" the normal layout and a split vertical stagger board is a compromise ergonomically and not really worth it. My reasoning is that a layout that is somehow similar to the normal "block" will require retraining your normal typing muscle memory, whereas a design that's very different can be "separated" more easily, so you're learning a new set of typing muscle memories, so it shouldn't affect your normal typing as much during the training period.
Thumb buttons / split spacebar are a definite improvement, though, and well worth doing, since it gives your "other" thumb something to do and makes Fn layers much easier to access, while still being able to hit all the keys as you're used to (since the thumb was doing nothing on the normal layout). If you have a gap on the bottom row, try to put it between where your thumb can reach easily and where the pinkie can reach easily.
