No matter how high the chances of success, the business is still a gamble and the actual odds are unknown. Most entrepreneurs think they have a sure thing, otherwise they wouldn't go for it.
Equity entitles people to reap the future rewards of a company. These rewards come in the form of profits and/or the proceeds of a sale.
No matter what the situation, there is a universal answer: a person's % share of the rewards should always equal
that person's % share of the risk taken to achieve those rewards.
If the game was Blackjack, instead of your company, and you and I each bet $1 we would each be entitled to 50% of the winnings, if any. We each took equal risk and deserve equal rewards. Things rarely go as planned, however. If the dealer deals two aces and we split, additional bets are placed. Let's say I'm broke and you put down $2 more. Now the 50/50 split is no longer fair. Your risked $3 and I only risked $1. It would be fair for you to take 75% of the winnings, if any, while I should take 25%.
When someone contributes time, ideas, relationships, supplies equipment or anything else to a startup and do not get paid, they are, in effect, betting on the outcome of the company. Just like in blackjack, they should receive a slice of the rewards that properly reflects their slice of the risk.
The amount people risk when they contribute is equal to the fair market value
of the contribution they make. So, if a guy can make $100K doing marketing and works for you doing marketing for free, he is risking $100K.
So, to answer your question, you should disregard your level of confidence in the company (because all entrepreneurs are confident) and instead look at what people risk. No matter how confident you are, it would not be fair to take a slice of the rewards that was disproportionately high. It's not fair to benefit from someone else's risk.
If you're sure you're going to succeed then pay everyone who helps you out of your own pocket. Empty your savings, mortgage your house, sell your cars. This gives you all the risk and entitles you to all the reward.
I've written a book about how this works. It's called Slicing Pie and you may have a copy if you contact me through SlicingPie.com
Good luck! Sounds exciting!