Use the HELOC on cash-generating opportunities like flips, then use the cash generated to buy long-term buy and hold investments. 

You are 18, you shouldn't be ready to buy a property yet.

2. how to know where to find a B,C,D areas\neighborhoods in cities\ countries.3. how do I know if a property is worth the checking\ buying?

And your net worth will thank you.If you still want to go ahead, you'd be better off buying a house than an apartment because, while the value of the building itself will go to 0, you'll still have the value of the land, bearing in mind that the land might actually lose value too given the depopulation and the yen depreciation.Sorry if I'm pooping a party but make sure you understand what you're getting into (which you're already doing by asking the forum) and then make the decision that's right for you according to your objectives.

Whoever buys your flip will also spend lots of time in this room, so it’s important to make it pop.

Buying a large new build home can also work well as a house hack as you can charge a premium rent, and generally most bedrooms built now a days have en suites (at least in my market).  

John Hickey congrats on buying a cash cow.

Investment Info:Single-family residence buy & hold investment.

Buy a quality property, stay away from the hood, rehab it as if you would move in, take your time picking a tenant, you'll be find.

I warn people over and over and over to know what they are buying and to go personally see what they are buying.