I work in the mortgage field, a few add ons.
1) HELOC are far and few in between now. If you find a lender to do one, likely it will only go up to 80% LTV now and require flawless credit in a non-declining market area.
2) A small HELOC (less than 50K ) you will usually pay closing costs. State dependent, but you need to put this in your APR. If you pay 1,500$ or 2,000$ in closing costs and keep it 5 years average that into it. You may be able to get nearly zero costs with a draw of over 100K, and even sometimes a prepayment penalty will lower them. (You can see draw backs on that.) The shorter time you actually keep it, the less costs make sense.
3) All HELOCs are tied to prime which is tied to Fed Funs Rate meaning it is variable and can change monthly and caps if they are there are in the 14% - 22% range. (state specific).
4) There are fixed second mortgages same credit/loan to value as Helocs. ALso if your 1st mortgage is over 5.75$ redoing your 1st, may still work better as rates are super low right now.
If you plan on paying it off in less than 3-4 years I would base decision nearly all based on APR. Look at the APRS, not the rates by themselves. (The actual cost of loan.) If you will be financing more than say 4 or 5 years, consult a financial adviser or CPA based on terms, rates, fixed, variable to see which meets your individual needs.
I am not sure this Disboard is the best place for financing advice.

I really think contacting someone who knows your profile is ideal. Welcome Home !!!