how does {HELOC / additional purchase Loans + debt carried} work?

[Janel Briones]

I am obtaining a HELOC on my primary residence to then use for the down payment(s) for investment properties, that I would also have an additional purchase loan(s) on.

What should I factor in, to decide what amount of credit I should apply for my HELOC - knowing that the purchase loan(s) lender would calculate my full HELOC amount within my carried debt?

Are there calculators or formulas that could give me an idea of how much debt I could carry (including my full HELOC amount) to obtain $X amount for my investment property purchase loan?

Is it fairly easy to go back and get my HELOC limit raised, if needed?