@Kelly P. I went through a period where I was trying to figure out how I can grab properties with no money down. It's a good thought exercise but I can't imagine getting a lender to approve of a scenario where a borrower is leveraged 100%.
"You're only limited by your creativity" - a quote that has stuck with me for a long time.
Based on the text in your post, it sounds like the seller has not received any kind of offer from you yet. So we're starting from scratch.
I personally think you should present 3 offers. The terms of the offers are completely up to you.
You mentioned that you have access to cash, HELOC, and have a solid w2 income. So I think you're in good position to present many offers to them and show that you're a qualified borrower in the event they provide seller financing.
You can still present a seller financing offer. You will just prolong the need for a traditional lender to enter the picture. If you like the deal at retail price, why not offer something like $5k down so they know you're serious and you take over the payments with a balloon in 10 years?
First, I think you need to have a conversation with the owner figuring out if seller financing will even make sense to them. If some big expense came up and they need 100% of their equity, then the mental gymnastics you're playing now don't matter since they won't be open to seller financing. But if they're cool with getting their payout at a later date, then why not offer to take over the property and give them a balloon in 5-10 years for an agreed upon price.