It's great practice to go through these analyses in order to learn the numbers, and the ins and outs of investment real estate. However, there are a lot of holes in your analysis:
1. What makes you think the seller will (or can) hold a not for $1M? (How much do they owe on the property, that will be a limiting factor). Check out https://www.biggerpockets.com/...
2. The seller is highly unlikely to take $300k below asking, let alone do that and offer $1M in seller financing.
3. You are highly unlikely to find a commercial investment property loan at 20% down and 6% interest. Commercial financing is going to be at least a point or two higher than the prevailing rate for homeowners, and will be much more focused on the debt service coverage ratio (DSCR), which in your analysis is around 1.0. Banks don't lend on "break even" scenarios. They want a DSCR of at least 1.25. Which means with $6k in NOI, you can afford debt service of $4800/mo max. Typically, the only way to get there is to put more money down.
4. Likewise, the seller is not going to want to hold a $1M from a poorly capitalized and overleveraged buyer.
5. The lender (and common sense) will require you to have some cash reserves going in. Even if you could buy it with these numbers, you won't be bringing in any cash flow on this deal, How will you pay for a broken HVAC or other surprise repair or capex in the first year? I realize you have budgeted for maintenance and capex, but if will take time to build up those reserves - What happens if you need a $10k roof repair a week after closing? It happens. And then you'd have to choose between fixing the roof, or paying the mortgage. This is exactly what the lender seeks to avoid when underwriting the deal.
6. Closing costs are likely to be much higher than 1%, and you'd have to fund your insurance and possibly property taxes up front (either direct to the carrier, or through a mortgage escrow), which, again, requires liquid cash.
7. You'd also have a conflict between your lenders on their mortgage position. Neither of them is going to want to take a second position lien. The bank could not, the seller likely would not.