I made a general questions thread earlier and it now seems be stickied (thanks IJ) so hopefully people with small questions can drop in there if they don't feel like making a whole thread.
This isn't really about minimum system requirements for your purposes Kalli, but a small contribution to the subject of Decker's RAM consumption. I have two Decker windows open currently and this is what my Task Manager shows:
The top one is a small deck with a few doodles and experiments.
The bottom one is a larger deck (about 100 cards / 3.5mb) that's been open for a week and has a pretty long undo history.
For the sake of experimentation I closed and reopened that 100 card deck and it's now only using about 70mb of memory.