Prelaunch campaign idea that works

we plan on launching our photo sharing community platform by January. So l plan on using a giveaway to incentivize the first 100 users that signup and makes a post. My ideal prelaunch strategy is to send my lead to join my watsapp group ,warm them up then for few days and then announce our website with them on launch day with the incentive.my partner idea is different from mine.he insist on sending them to the website directly with the incentive. His reason being that we aren't selling a product rather a free platform that anyone can signup.
So what is your take on this.send the lead to join my watsapp, warm them up and announce our website on launch day with the incentive,or send them directly to our website with the incentive.