Welcome to the forum! You'll certainly get a lot of help here for building robots. If you are looking for some advice on building antweights, I'd recommend this site: http://robotwars101.org/forum/viewforum.php?f=1. This is where most of the UK antweight builders post their updates, and it's a very useful website all around.

In terms of antweight events the three main ones would be the Antweight World Series, the Bristol Bot Builders socials, and the recently created Roboshowdown. They're scattered all across England, and they usually post info about them either on Facebook or on the RW101 site. Hopefully this is somewhat useful.