I usually only add my own Sims into a gameplay if it is a fresh off the boat gameplay. If I add any after the gameplay is established then only for story purposes other than a possible mate canditate. For instance in my favorite gameplay I plan on introducing the Altos into that gameplay, give them all (except one) an undesireable traits, give them a horrid ultra modern manion to live in and plant them into the Goth neighbourhood to create a sort of neighbourly dispute thing.
The Altos really won't like the dark and dreary Goth mansion and the Goths (and probably the other neighbours) will not like that modern monstrocity around their beautiful victorian mansions that is the trademark of their street.
But introducing new Sims into an established gameplay is never to find a cupid's match unless the cupid finds it anyway. If it is a new save I might create a couple to play with but usually its either a single or a few singles in a roomate situation. My favorite gameplay for instance only has 3 sims that I created (so far, the Altos are not yet moved into the hood). A single lady and a couple, not created at the same time though. The lady is now married to J. jr. and they have a little girl now.
That is usually what I have done in my Sim games. Rely on premades and townies as a possible candidates. The only reason I add new Sims into an existing gameplay is to add to a storyline that is usually not of the romantic type. But like I said, the Sims do at time have a will of their own and choose a mate that I had not planned for them.
