you can create humidity in the house.you can use a humidifier& a smaller room would be easier to control that,but thats usually the bathroom(though mine is 12x12,not really small) you could mist your
tree& you can give extra light buy useing grow lights.I know the type you chose does tolerate cold well(I've been reading up on um)If I was to grow a dwarf variety.I'd use a south faceing window turn it every 3 days& keep out of drafts(so would need something to block air from window sometimes that was easy to lift on*off.piece of cardboard)My bedroom stays around63-68 but some days the sun warms it pretty good.I do have a row of milk jugs with water in them along wall under window& keep
plants close together.I wish the windows were larger,but he probably did that for a reason....ME
I grow a ponderosa lemon
tree.sometimes the leafs curl on it when low on water or temps drop& freezes will have it loose some younger leaves.I don't have a humidity problem here.ours is too much,the woods just makes it worse cause of all the
trees,so my
plants are happy,but electrical tools ain't.
This is page I saved
http://www.hort.purdue.edu/newcrop/morton/calamondin.html When I looked around on those type.I found "changsha" to be the cold hardiest.its took temps to -5& recovered in Rio grand valley TX& is sometimes used as rootstock.Course I'm checkin into TX type grown.I think you have less humidity there. It mentions a shipping temp in dark storage of 53 for 2 weeks.
http://aggie-horticulture.tamu.edu/extension/homefruit/citrus/citrus.html That one is more TX stuff but has some great
growing& preventive measures.I couldn't find any pics of fruit setting,But grapefruit gets a dot
growing when loses the
flower and a fruit forms.