"Conservative" being mentioned in a PPM or presentation (especially repeatedly/often) with only anecdotal justifications at best, can quickly be a yellow flag.

If your parents are paying $1300/month for a 2 BR in Los Angeles there is no financial justification for considering giving that up to convert a garage into an ADU. 

There is good justification whether yes or no.

Your depreciation expense will be a function of the value of the improvements and the method you use for calculating depreciation (e.g straight line vs accelerated).As long as you have good justification for how you separate land + improvements, you are fine. 

What justification is there for the ongoing annual fees for the life of the plan?  

Frankly, if it costs a landlord $25/month to get the protection they need, then there's really no justification for charging more so yes I agree that charging $50/mo in that case would probably get you into hot water.

Each time, I would just if they wanted to leave. 

There was absolutely no justification for this.

As a landlord there is no justification on your part to give people a second chance.

These are created by the property and therefore have a justification to survive.IRS liens are created by the previous owner who is wiped out - not the property - so IRS liens do not survive tax sales or foreclosures.As for the HOA fees surviving the tax sale, I think the precedent is that a tax sale is a break in chain.