I've done surface research, but was wondering if anyone has found success with it, or any obstacles in its use. 

I think this is the biggest obstacle, in the end - who better to invest in than yourself. 

Moreover, the construction of the detached ADU is going to cost me around $250k-$300k cash .

It is why our plans started with the more expensive detached ADU.  

An obstacle I'm running into with building my portfolio after analyzing a potential deal is the very high property taxes, particularly on properties that have been owned a long time by the previous owner.

>California allows one attached ADU, one detached ADU, and one JADU on primary residence.

Remarkably, despite these ongoing shifts, delinquency rates remain low on a relative basis when compared to the office, retail, and hospitality sectors.Although factors such as declining household formations, rising supply deliveries, and weakening demand may present temporary obstacles, the sector has successfully emerged from similar challenges in the past.

If you have contacts in the U.S who you trust to invest with, this could be the way to get around these obstacles.

I know you said you’re also new in REI, do you own any properties and if so what would you say was your biggest obstacle getting started?

I'm working on converting a 2-car detached garage into an ADU in NC and going through the permitting process now.