Pros and Cons of Buying an “add-on” unit through an entity

[Seyi A.]

Hi BPfam,

I am considering purchasing a neighbor’s condo that’s across the hall from mine, and combining the two into a larger unit but keep them as two “legally” separate units.  The neighbor’s unit is owned free and clear, and I am considering (for various reasons) asking if he would consider offering seller financing (promissory note, ammortized over 30 years with a balloon payment at the end of year 5).  My questions are:

1. If I purchase the property through a land trust that's owned by an entity (probably an IL LLC owned by a WY LLC for anonymity, of which I'm the sole member), would the property tax and interest deductions flow 100% through to my personal tax return? Since my local and state personal deductions are subject to the $10k cap under the new tax law, would this be a way to (legally) circumvent the cap?

2. If, instead of a Seller-financed mortgage, I opt for a traditional mortgage (assuming I qualify based on this ownership structure), would my lender restrict me combining the two units?  Or do you think they would insist that the mortgage be held in my name?

3. Would I be able to refi both my existing mortgage and the new one on the other condo, whether Seller-financed or financed by a traditional lender, into a single mortgage covering both properties even if they are still two legal properties?

4. Are there are any other restrictions/pitfalls that I should be aware of in pursuing in this strategy?

Many thanks in advance BP fam!

Seyi