What To Get Next?

One thing stands out from that list - you need to get at least 4 more sterbai cories and 2 more otos. Both of these are sholaing species, and cories in particular need to be in a fair sized group.

Once you have increased those fish numbers, you will be fully stocked.

Cories prefer their own species but if necessary another species of similar adult size would be OK.

With two cory species, should you ever have eggs that actually make it through to adults there is a possibility of them being hybrids. Should you ever have fry grow up in your tank and you want to move them on, you would need to make it absolutely clear that they could be hybrids. Passing hybrids off as pure breeds is highly frowned on.

You seem to have hard water and soft water fish together...

Rams being soft water and the livebearers being hard water.

I'd advice thinking about matching any future purchases to your water parameters for better long term health.

My meaning is not to have a rant but to give some steer for which way to go with your stocking...

My electric ram

Degrees clark 18, degrees german 15, calcium carbonate 260ppm. Does that help

I've got some tetra kh minus so I might give that a go

Thanks sue