Depending on the county, the assessor will pick up your sale price and adjust your taxable value to 70-100% of sale price.Insurance: Have your insurance broker get you a soft quote based on your lender's insurance requirements.

They are not as scary as some make them out to be, you just want to be certain that you can regularly contribute to the principal of the HELOC/home equity loan (on top of your monthly interest only payments), so you can pay the balance off within a reasonable amount of time. 

But if you are using seller financing and a regular CRE loan, the seller will need to be comfortable subordinating.

If you are local check up on your contractor regularly. 

Most investors I work with do either a regular refi DSCR loan or, take up to 75% or 80% of equity out of the home through a cash-out refi. 

I would start off by getting several quotes.I can tell you that my regular AC guy charges 40% more than the guy I go with.  

It looks like your seller wants to seller finance the deal to 'be the bank' - which can be great - maybe you can negotiate a better deal on interest rates than what is currently going on in the regular market - which would be awesome.As for which home first - I would definitely go for the duplex you are already in.  

I invest regularly in Worcester, Providence, and towns outside of Worcester. 

Using basic numbers, assuming I sell a property for $10M and after cost basis is accounted for and mortgage is paid off, I have a net taxable gain to me of $3M.I'd like to purchase a rental lake house property for $1M (funds coming from that $3M taxable gain). 

Banks do this regularly during any kind of financial hiccup.