You should not use account types. It is better and more flexible to use a profile field for sexual orientation. In this way, in the search engine you can select the options you want.

It is very bad practice to show an empty search result or with few results, you would have to make a plugin that in this case would suggest friends of friends who are not your friends. There is already (or was) a plugin that suggests people but it is very poorly done, it suggests people who even have several blocks of friends of yours, it does not take into account if you have already visited their profile, if there have already been private messages, if they have photos and the filled profile ... and of course it does not link to the search engine nor does it take into account the distances or the age of the people.

Maybe I will develop a more powerful search plugin for dating sites because what we currently have is very primitive. Perhaps instead of an ugly form, only "people we think you would like to meet" and if you don't like what it presents, it will encourage you to improve your profile. The idea is that each time you access that section it shows you a minimum of 50 different people ... or ordered in another way if the website has few members. Nor is it good to let them see the total list of members and know how many there are, it is better that they entertain themselves by searching and visiting profiles.