Fsbuild-2 Flight Planner

I just recently started using Fsbuild to create flight plans for FSX and have learned the basics but have a few questions about the more complex aspects. Before using Fsbuild I usually would just use the default planner and just go direct via the GPS even though I knew it wasn't realistic but I didn't really understand how to create more realistic flight plans. I tried searching but didn't find anything so I apologize if these have been asked before.

1) How do I calculate the amount of fuel I need for a specific flight? So I'm not overweight when landing. I understand I might have to create a burn table but not sure how to figure out the number for the boeing 757-200 from Just Flight.

2.) I created a flight plan from Anchorage to Los Angeles and used the SLI1 Star. After the KSMO waypoint the next waypoint is Klax. How do I setup the flight plan so that after passing over KSMO I will head past Downtown LA and then back around for a landing on runway 24R or 25R. Or would I have to fly that part manually entering headings into the autopilot.