Hi bobbybubble So you want to have ago at keeping goldfish I hope that's not because you think they are going to be easier to keep than tropical, as you will find out they are a lot more work, but worth it, It depends on what type of goldfish you are looking at keeping, regular goldfish, comets, shubunkins or fancy goldfish like fantails, Black moors, telescope eyed or orandas etc, I would keep the same type together as fancy goldfish like their water slighly warmer than the regular goldfish also you can have problems when the fish are in spawning as the male regular goldfish can mistake the round bodys of the fancys for females and harrass them which the fancys can not handle. To know how many you can keep you will need to work out how many gallons your tank is and allow at least 8 uk gallons per fish for growth unless you plan on getting a larger tank as they outgrow the one you have
Glad to hear you are taking it slowly as there is no rush, and I wasn't being funny its just that some people get goldfish thinking that they are a lot easier to keep than tropical because you do not need a heater, but infact they can be more work as they are very messy fish, what type of plec are you thinking of getting.
I am not really sure what would be suitable for a coldwater tank because a lot of plecs grow too big, there are brislenose plecs that do not grow very big but they like a warmer tank, I have 3 hillstream loach they only grow to about 4 inches they are meant to eat algea but I find they only eat what grows on the algea. Here is a photo of my striped one :
You say you have just got 2 black moors, how long did you set the tank up for "cycle" before adding the fish and do you have any plants or decorations at all as they help to make the tank look less empty with only the 2 fish in it, I would wait untill the water parimetors are stable before adding any more fish. I guess you know all this already with keeping tropical before.
I had the tank set up for a week with a few plants. I took a sample of the water to the Aquarium shop and they told me it was ok to add fish. I thought I would add about two fish a week(to a maximum of eight) is this ok.