What does it actually take and need to start out a new sportsbook/casino/dice site?
You'll need money and lots of it. you have to hire coders, advertise. it'll cost you a lot to keep the site up and running, it's not an easy job as many think it is!
What amounts needed to start up, what providers for themes/scripts all that stuff etc?
Depends. if you want to run a site with max win say .5 BTC then probably 100-200 BTC(i think). it's best to hire coders to develop custom script/site.