Your question has been pretty well covered, above, but I'll just add that I find an advantage in using stainless steel. I have a stainless steel stockpot that I mix my oils in, and a stainless saucepan for my lye. What I like about SS is that it transfers heat well, meaning that you can assess the temperature of the oils or lye by feeling the side of the pot. I like to soap cool, so I wait until the side of the pot is just barely warm. Also, if you want to cool the lye fast, you can place the SS saucepan in a bowl of ice water. It's a small advantage, but one that I like. Also, because SS is not absorbent, once washed, they can still be used for cooking. I've been doing this for years, with no problems. I have a small house and a tiny kitchen, so space is at a premium. The sizes of containers you need will be dictated by the size of your batches. I use the regular stockpot for smaller batches, but I have huge one for when I master batch. Don't know if you have Ocean State Job Lot where you are, but they have a variety of SS pots. Thrift stores are a good place to look, too.
Like others, I love the dollar store for miscellaneous soaping tools. It's always fun to discover new stuff there. Good luck to you!