Hi @Carmelo12 and welcome to the KNIME forum!
I just wanted to share a hint with you concerning your problem of doing hierarchical clustering in a very big set. Recently, @chiabell posted a workflow which could be of help in your case. It is a combination of K-means and Hierarchical clustering to cope with big sets of data. K-means does a first level of clustering and a hierarchical clustering on top of it does the rest. Just in case this could help.
With respect to the second problem, is there a reason why you need to specifically use the Pearson’s Metric?
Hope this helps,
Ael