I wouldn't mix the lakes. Some have different food requirements. Yellow Labs get a bit big for a 30g too.
Also, I would only have 1 type of shell dweller in a 30g. They are small but most are really territorial and I predict some might get killed depending on which you mix.
Multies are always a good choice. They form colonies so you could have twice as many as you started with in a matter of months.
Brevis are another small shell dweller, good for a 30g. They form pairs and pairs can be territorial, so in a 30g, I'd go with just a couple pairs...maybe 3 max. You'd have to watch them with the fry though because if they feel threatened, they'll kill the fry.
Occies are really territorial so you'd only be able to have a pair in a 30g (I know right!). Otherwise, the males will fight.
There are other not as common shell dwellers that would work too. Do some research. I would plan on choosing one type and then plan other tankmates to suit them. Some of the
Julidochromis species would work.
Make sure to do a site search for tanganyika
tanks if you haven't already.