The simplest Welding-shop equipment that permits you to perform your work is probably all that you need for getting started. For work on low carbon steel an example would be a simple AC transformer welding power supply. Keep in mind that used and reconditioned equipment may be available at substantial savings.
Fancy looking machines with all sort of additional capabilities may be strongly promoted by suppliers, but the question is if they are going to help your business become more productive and successful. New equipment should be first rented or leased for a short while, to decide if it actually provides benefits.
Besides electric welding equipment, an oxyacetylene welding kit mounted on a hand cart holding two gas cylinders is almost a must for any Welding-shop and maintenance facility. An air compressor may be needed to power pneumatic tools.
Apart from welders you will need accessories, like disc cutters, grinders, welding table with a sturdy vise, files, hammers to remove slag etc. and of course personal protection devices like welding mask, goggles, gloves, apron and so on. See