On the topic of Silverwood Trees and Nodes... To speed up the process, do a lot of transmuting on the node you want to convert over to pure, before merging the Pure node with it. The thing is, it's not the max size of the node that's taken into account with the merge, but the current size. So, in theory, you can make a 600vis Dark Node into a 6xx Pure Node by merging it with a 20vis Pure Node from a newly-grown Silverwood Tree, as long as the Dark Node was below 20vis when the merge occurred.
In practice, it's better to be safe than sorry, and get a larger max size Pure Node anyway. If nothing else, because of the fact that the Crystal Cluster requires a big amount of power, so when you use it to move a node, if it's a tiny node, it'll take forever...