Does anybody knows aftermarket wheels ET for 20VT?

Lets say If original wheels "15 or "16 turns in the middle of wheel arch along the chassis, then what exact ET should be on "17 wheels without (or with) spacers for Brembo brakes?

The shape of the inside of the wheel is more important. You could technically run any ET.

Agree shape very important, but you should be fine with an ET of between 27 and 32.

You want to be looking for wheels as follows:

PCD - 4 x 98 (4 x 100 is more common, but then you need wobbly bolts)
ET 35 (but preferably less as above, because otherwise you can have very little leeway before it catches the Brembos)

You could use spacers, but personally I'm not comfortable with them, probably irrationally but nit her of my sets of alloys have needed either spacers or wobbly bolts and I feel happier that way.