The game is going to have 4 players. Doing combat with 5-6 players seems like it would be a bit overwhelming. Plus, I like to get to know the people I game with.
400 BP standard build, core books include SR4a, Arsenal, Augmented, Street Magic, Unwired, and Runner's Companion. If you want something outside these books you must ask first, and it should have an interesting backstory otherwise it'll probably be rejected.
I'm going to allow characters to have free contacts up to Cha*2, but there's a catch. Since they'll be traveling outside their home base of Seattle, contacts should be appropriate otherwise they'll be wasted. Local Seattle gang contacts will be virtually useless for this adventure. Useful contacts will include information dealers, international smugglers, etc. You won't need a Fixer contact.
There are some severe restrictions on what gear characters will be allowed to bring with them. It's going to be on a case-by-case basis, but don't assume that you can bring a Panther XXL, 30 lbs of plastic explosives, flying combat drones, etc. If you have a question, ask. The limitations are based on weight as well as size. Spoiler alert: you'll be traveling via small aircraft at some point in the mission. There is some good news, however. Once on-site, characters will have the opportunity to get their hands on some gear (for a price). The gear listing will be provided by me and will include a motley selection of weapons, armor, etc. Some if it will have modifications already applied, some will be modifiable by a local armorer, and if you want something truly specialized I'd suggest picking up a basic armorer skill.
