Wheel & pedals are very important to consistency and finding an edge but to get going, a basic setup will suffice.
Sign up and pay for your membership, there is usually a 3 for 2 offer. Run the mx5 to begin with and earn your stripes essentially. Lots of practice and focus on clean racing. Speed isn't everything in racing or iracing. In the rookie series particularly, cleanliness will get you up the licence classes far quicker than speed.
Watch the video tutorials for anything you are unsure on.