Using $70k from my HELOC to invest; is S&P 500 the best strategy? Want to confirm deductibility + risk/reward outlook

Hey everyone! hoping to get some guidance from those of you who’ve used a HELOC to invest.

Here’s my situation:

• I have a $70,000 HELOC at ~5% interest (Scotia STEP), and I’m sitting/waiting on the right deployment.
• TFSA is fully maxed (~$88k).
• I’m considering putting into S&P 500 ETFs and maybe a few dividend or global ETFs for diversification.
• I plan to invest via Questrade in a non-registered account, so I can deduct the HELOC interest against my income (which I believe is allowed if the investments generate income or capital gains).
• I’ll cover monthly interest (~$290/month) using personal side business income, and I’ll keep the excess cash not used in interest payments as a cash reserve in a high-interest savings account as a safety buffer/general reserve fund.

Trying to confirm:

1. Is this tax deductible with this strategy?
2. Is S&P a safe route, especially if I do not plan on taking these funds out unless in an extremely opportune scenario - ie, remain invested for at least 10 years and continue leveraging HELOC into this portfolio as mortgage principle is paid down each month.
3. Has anyone actually doubled a portfolio doing this or at least seen sustained success?

Open to all thoughts and ideas and criticism. I’m quite calculated in terms of risk.

TL;DR – Using $70k HELOC at 5% to invest in non-reg account. TFSA is maxed. Leaning S&P 500. Want to confirm deductibility and best way to grow long-term while covering interest via business income.

[EDIT] formatting.