By all means plant both of the ones you mention they are both great shade plants. The Lamium is a very fast grower. Hellebores are beautiful, but I am new to those and only planted my first babies last fall. (tiny from the plant trade so they are still very small.) I did also buy one this spring and it seems to be doing well with little fuss.

I looked at your photos. That is a great space. My first thought was that with that huge tree trunk (oak?) you need some big plants first to make the transistion in size. What about a couple of nice big Hydrangea bushes of some sort? The Lamium is a great fill plant to brighten up spots between lots of green, but I think you might consider planting some large leafed hostas such as a Sum and Substance or other dramatic plants like Japanese Aralia. There are a lot of options for shade now. I see you have some great lines already established with the monkey grass I would go ahead and buy some lamium now because in a year you will have enough to move it around. There are a lot of great sources for inexpensive hostas, just go for a variety of colors, sizes and leaf shapes for the best effects. The ones you planted are not noticible but in time they will grow bigger I am sure. The same is true of the ferns.

There are tons of great books available at the library on shade gardening with wonderful photos. My library is online now so I can search their database from home and request books and just pick them up when they are in. I always have a stack of gardening books on the nightstand. It is a great way to spend a rainy day as well. Good luck, that is going to be a great spot.