The word flipper has certain connotations associated with it that may diminish the brand of the site from certain American end users or companies. If your demographic is other resellers I say go for it. I don't want to be a Debbie Downer but you asked for honest opinions.
Not a big fan of the word "flip" as it implies buying something to resell later for a profit. A brandable domain marketplace is for people and companies buying a brandable domain name to establish their business, not selling domains to other domainers.
If you're looking to sell to an end-user, CovetedBrands is your best choice. BrandFlipper is actually a good name but since it's more on the reseller side, I won't expect that much money for it.
I voted on option 4. In my opinion if you have a brandable domains and want to flip quickly with domainer and investors. This could be right place for that. However mostly the site depending on service you are offering. If you offer or implement right services. the domain name doesn't mattet anymore for domainers. They will find it anyway.