Honestly, the Conference, Weekend, and Lone Star (Saturday) badges are all great! With the Producer's badge you get access to all the parties. Saturday is absolutely stacked when it comes to the conference. All the exciting panels are then. The networking parties are exciting enough, but you meet the same people waiting in the lines outside the venues. The highest I would go is Conference. Remember, even if you drive to the festival each day and save on the hotels, you still have to worry about the price for parking, food, gas, etc. You might want merch! The weekend badge is great, the Lone Star is solid. If you have that Friday off, the Conference badge is worth it!
Volunteering for SXSW is such a good idea! It sounds like quite a year you have planned. A
couple novels, a studio crew certification, and contests? This year is shaping up to a win for you as a writer! Pitching scares me too
Oh, last thing about festivals. Be careful when submitting. It's easy to get trapped in excitement of earning 25 accolades on your script but these are quite literally money traps. Some competitions are scams, so only submit to a festival you feel has something to offer (reputable judges, valuable feedback, networking opportunities, a deadline, etc).