Hi man and props to you for this mad project.
About your oil problem, here is my story, it could give you some ideas : i just finished a redblock build with an HY35. Basic support mods.
Removed the breather box and replaced it with a plate and nipple, with a hose that goes upstream of my turbo inlet.
First start, smoke everywhere in the garage and after driving a few miles, an engine bay covered with oily dust.
I thought : engine must not be oil proof, lets change every gasket : cam cover, oil filler, oil dip stick.
I started the engine : i literally smoked out the whole block. Worse than before.
I tried to unplug the turbo oil return to see if the drain was clogged. At idle, the flow was flushed fast enough so no problem here (or so I thought).
Next test : i let the breather hose comming out of my custom nipple, vent to the atmosphere.
Problem gone.
Now my analysis is : bottom end was seing some pressure (unknown milage engine).
At first (old gaskets), some of this pressure was pushing out through the gaskets, giving me the oily engine bay.
Then it hit me : when i changed the gaskets, the only way this pressure could exit was the turbo. The pressure was getting to the turbo through the oil return.
And this is why, when i started it again, there was much more smoke comming out the exahsut, and more oil in the turbo inlet and pipes.
So you might wanna give it a try, venting your engine to atmosphere, while giving it the beans.
Another thought : my turbo oil return is too small. Holsets love oil and i should have gone with a 19mm ID return, where i went with AN-12 which is 16 iirc.
Another thought : your turbo could also be pulling oil from your breather system. Be sure you have some sort of chicanes between the block and turbo inlet. I am sure this also was one of my problems.
Good luck. I am really interestd to see how it ends up.
Great, great car and attention to detail.