It sounds ideal. I would mix conifer fines and/or sphagnum moss with the soil and mulch very well. Also, just on general principles, I would mound the soil slightly and give it a little elevation. Probably not necessary, but it won't hurt either. It will need some sun to promote blooming, especially in the spring and early summer when days are long anyway.

I had trouble finding viscosum, so I got a Weston cross from viscosum, 'Lemon Drop'.

I have several plants of a pink selection of viscosum planted in both a sunny wet spot and in a shady average moisture spot. I have found that the sunnier plants bloom much better than the shady ones and are a bit more compact. So you may find that with that little sun, they may not bloom well. They do have nice autumn color.

BTW I have Lemon Drop as well, which is a lovely plant, though the color is more salmony that lemony to my eye. I hadn't realized that it was a viscosum hybrid, and have several planted in a dry spot in half shade, but it does quite well in these circumstances.