Dicksonia Antartica like damp conditions. They will do well in full sun if they have damp feet. They grow largest fronds in semi-shade. The trick is to keep the crown (the bit were the frond emerge) damp at all times. More of these ferns die from drying out than frost. I would repot in a larger pot, add in lots of good compost mixed with chicken pellets, soak the trunk and keep the crown damp. A seaweed feed every week in summer will do it all good.

For the fungus, just remove it. You often get weeds growing on Dicksonia trunks and crowns.

If you get cold temps (below -3C) then cover the fronds with a fleece, very cold temperatures then cover with an old duvet or bring into a garage/GH.

I totally agree with Botanic. If you want to plant it out in the future then choose a sheltered shadyish spot. Once in the ground you won't have to worry about it so much - just keep that crown damp in dry weather and cover in extreme cold. I have one I planted out from a 5cm pot - it is now 14ft tall and all I can see out of my north facing window - but I can't imagine a better view!
Another thing to remember is that they don't like you playing/handling the fronds - they will tend to brown and die off - so even tho' they look very tactile - try not to touch!
I have violets and other plants growing on the stem - I occasionally remove them - but see them as a sign that the stem is healthy - damp enough to support other plants...