@Bakafish it might be helpful for you to give a quick overview of the processes/challenges involved in shipping components to where you live in Japan, for those who don't know. It'd be interesting for those of us not in the know to give you better advice. What's the VAT? Any arbitrarily low weight limits that necessitate freight shipping? How does freight shipping work? Etc.
Unlike the other issues you mentioned, shipping is a little more straightforward. Size/weight/VAT/import restrictions/cost are the usual considerations. As far as I've experienced, as long as all that checks out it doesn't really matter what's in the box or where it comes from.
When you say the steel plates are more expensive it'd be helpful too to know what those plates look like, and what you were quoted. If for example you're getting quoted $100 per flat steel part cutout, that could be reasonable. If you're getting quoted $1000/ea, maybe not so much and we can point you to a better supplier that will save you $$$.
Lots of interesting and capable suppliers out there, I learn about more of them every week. Fabrication capabilities are improving at a rapid clip, stuff that was crazy expensive even 5 years ago is reasonably priced now. Some stuff that was unobtanium 10 years ago is cheap today. Flex and HDI PCBs are an example that shocked me, literally a 10x+ cost reduction over the last decade for prototype quantities, and more advanced capabilities to boot. Promise I'm not badgering you here! Genuinely think you could pick up a few great tips/new suppliers to play with, if we had some idea of constraints/BOM costs/etc you're working with. The people who get a high from saying
"toy machine har har" will get bored soon enough.