So, which point could be other bottleneck? If minimum $10k is too small, what if minimum is $30k?
IMO $30k already gets you something that can also bring rental income and your renter will live in decent enough conditions to consider paying their rent + continue living there
rather than living mid year or mid contract.
But one question, considering you found those cheap houses in rural areas in Japan, why not invest in them?
You are already familiar with the environment and don't need to go international until you do it locally
From experience, when going internationally you will have different rules and obstacles different from country to country. If you go in the US or the western Europe, you will find that the way to go is to take a loan and invest it in houses. The business works here and that's pretty much how it goes.
Example;
invest in $1m apartments with $750k loan and 25% down ($250k deposit), preferably
interest only if you've got the credit, with 3%
Let's say you get 6 apartments rented for $800 each (going conservatively)
$800 x 6 x 12 = $57,600 a year
interest only rate = 750k x 3% = 22500
57.6k - 22.5k = remainings for fees and income
After 5 years, if your house did not depreciate you can sell it and pay the bank (remember you've got an interest only payment type of deal)
Alternatively you can go for "repayment" type of deal but that increases your monthly costs and minimises your bitcoin investment.