For this reason, it’s important that the self-directed solo 401k maintains enough liquid cash in order to cover expenses such as HOA dues, property tax, etc.

In the 2nd cases the mortgage was fine with equity present, but it needed about $10K in rehab and they were $3K behind on HOA dues.

Zillow is giving me an estimated mortgage payment of about $700 a month, including taxes, PMI, insurance, and HOA.

HOA is 293$.

If I make a cash offer I should be able to buy it for about $55K, It will rent for $1250 per month with $40 monthly HOA fee. 

Including taxes, HOA, insurances and especially a property manager cost as I have to make that investment fully passive (no active income allowed in my situation).I have experience in rental in my home country but as there are many differences (both financial and cultural) I just see myself with that project here as a newbie.

Unfortunately, the HOA fee has also since risen to now $155/mo, but I'm still way ahead.

And i wonder if they wipe out past dues Kind of like when i buy trustee sales in Oregon the HOA fees that are due are wiped out and start anew.. 

This is ok, assuming it doesn't violate your HOA bylaws, local laws, and occupancy limits.

I succeeded when I had my issues by having a very hard line about... if there is an issue with legal infractions, please call the police if there is an issue with parking please notify the HOA.