Don't get sucked into all that crap that the mail order houses try to sell you. If you do decide to need them, it won't be until the aircraft is completed, so you don't have to order them right away.
The kit will have a list of what is really needed included with it. You may be able to find all the info at SIG's website. If you have a local hobby shop, you go there and see the kit for yourself, and get some advice about what is needed.
All you really need to get started is the kit, CA glue or white glue, 30-min epoxy, a hobby knife, maybe a hobby saw, T-pins, sandpaper and some small clamps or clothes pins. You can get a long way into the build, and then decide what you really need.