I want to buy a house for myself in the next year, I’m worried that taking on the debt of these apartments will reduce my buying power.

By standardizing and buying in bulk, they are able to reduce material costs.

If you can get seller to reduce price due to not vacating a unit, sure that would be great.

I'm hoping he might reduce the cost in exchange for a longer term.

House hacking is definitely the best strategy for anyone looking to significantly reduce their living expenses.

I'm considering developing properties and using pre fab home kits to reduce build time and keep the money moving. 

In the latter scenario, you don't cash out the investment property to repay the primary cash out; rather, you cash out the investment property to buy another investment property.One more thing to keep in mind - when a heloc and the market turns, the bank can reduce the balance of the line, reducing your purchasing power.

If you come in under budget, most likely the bank will just reduce your loan balance, potentially when you refi the construction loan you could get cash out, but I would not bank on this.

Since it is a long-distance investment, we do want to keep certain cash flow to reduce the risk.

You've reduced your cost of living you're also putting your money towards paying down the principal which is increasing your net worth.