One of the bedrooms on the ground level is currently my office, and I was considering keeping the desk, and buying a monitor & docking station.

We help with management and boots on the ground. 

We are trying to purchase rental properties to pay for my children's private education.

If I was interested in purchasing a seller financed home with the total price of say $700,000, could the loan be structured to pay off say $150,000 to the seller over a 4-year period with the remaining due after that period?

I do pay large down payments to make sure the LTR play still would work if need be, but run them as rent by room (Co-living).

In 2020 the house was 75% done and I had to re appraise the house and get a new loan to pay off all my credit cards, personal loans, etc.

And it goes without saying that the broker should be paying for your time for this because as @Marc Winter made clear it is their job to be showing. 

I am a strictly ground up developer.

What would the boss think about the idea of taking that $200k and investing it into a cash flowing property or properties, and using that cash flow to pay for your Crest vacation a couple times a year?

Other than paying the lump sum...