How complicated is seller financing?

[Eric Mcginn]

As far as permits and renovations and ADU additions?

We are in Lake Balboa in the City of LA.
I'm considering giving my landlord an offer to buy before we move. I know that’s weird but we’ve been here for over a decade, know the market, and know there’s money to be made if we make the right deal. 

I've never done seller financing, but it's the only way the deal really work for me. I'll want to rent it out to other people and possibly add an ADU and do other renovations is this risky with the deed still in her name?

Also, I’m not into tax evasion necessarily but she’s owned the place forever and has minimal taxes. Any way to delay the official sale to keep taxes low while still maintaining a contract to buy? 

I’m almost hoping she rejects my offer because it’s so complicated, but it kinda seems like it could be a win win.

We pay $2600/month

I’d offer her $3k/month ($600k @5% 30year amortization) plus I handle taxes and insurance. Maybe a 7 year balloon payment and maybe a 3,2,1 prepayment penalty of something. 

The place is worth $700k on the market as is. But she’s in her 80s and recently moved out of state. So she’s really into just collecting her check every month which I’m faithfully sent her ahead of time for 12 years.

Anyways, assuming she accepts, does any of this make sense? 

Rent would be ~$4500 for the new tenants and the ADU could go for $2-3k if we converted the garage.

Thank you for any insight!