What to do with my K11?

Hi all
I am very new to this. Became a member last night!
So here's the story, my friend was raffling off a micra he had. £6 a ticket and I happened to win!
So now I have a little red K11 Micra Yr2000 celebration model sitting in my garage.
I have plans for this maybe next year if I have the money to turn into a little machine.
What I'm looking to know from you experts out there, what's the best thing to do?
Such as what splitters to use? Where can I get the wider wheel arches? Best alloys to fit it?
Pretty much anything you may have done to make yours a little better.
I also have the notion of putting in a bigger engine. Will someone please tell me the story on how this works?
What's the biggest engine size I can put in which is a straight swap? Without any need to change anything else?
Would I have to change Instrument Cluster, ECU, Keys ect?
Thanks in advance. I look forward to hearing from you all!