My first brew kettle is the economy NB 8 gallon one. I bought that over 10 years ago! I got creative drilled holes in it added a couple of nipples, sweated them in with silver solder, and it worked great, except…. once I discovered I need a vigorous boil, it wasn’t big enough. With that said, someone will ask how big? Go as big as you can afford, and for a 5 gallon brew I would easily say 10, if not a 15. You need room… Sneezles61