I limit either peat or compost in the 5:1:1 mix to 15% of less of the whole. I've used both & don't see a benefit from using compost, so I save it for the gardens/beds. ;o)

Al

I just happen to have big amount of compost and none of pet moss.

Do i need to add microelements or they can come from compost?

I would not depend on compost as a source of nutrients any more than I would depend on bark or peat. It would be my suggestion that you go forward with your nutritional supplementation as though your container media supplies nothing in the way of nutrients - unless you are approaching container culture from an 'all-organic' approach, in which case you'll have to piece together a list of organic soil amendments that are at least capable of supplying what nutrients are needed.

If you are using a soluble fertilizer like MG (or other) All-Purpose fertilizer and the soil you are using has been limed so there is a Ca/Mg source, you should be good to go.

Al