Few Questions From a New Arrival

Kinda new around here and have a couple of questions. I'm just starting to navigate my way though this place, and much is easily grasped, but a few things are perplexing and I couldn't find answers elsewhere. So sorry if this has been asked before, but ... 1. What's the meaning of the large font number in a circle on my user profile? 2. Is there a way to customize the default sub list that runs across the top of the page to replace them with personal preferences? 3. What is MODMULTI? 4. I selected to open links in a new window in my personal preferences and saved it. But they still open in the window I'm in. Is this function not available, or is there another trick I missed? Thanks in advance for any help. So far I kinda like this place.