TLDR:You don’t need anything to cast a spell except your intention and you do not have to cast a circle or protect yourself before every spell.
First off you don’t have to have anything to do rituals and spells other than your intent!
You can do spells in the Inner Temple or Mind Palace
or you can use the online Virtual Altar
https://forum.spells8.com/t/new-interactive-virtual-altar/33792
Whether you cast a circle or not is up to you. I don’t always do it. It depends on the spell or ritual as to whether I feel the need to do it. But short answer is no, you don’t have to do a circle before a spell. You could ground yourself first or mediate as alternative options. Or forgo it entirely.
If you don’t have the right ingredients, there are many items that can be substituted
You can also use pictures of items or drawings. There are lists of correspondences that can help you substitute one item for another.
As to protection, it depends on the spell and how much energy I’m putting into it. A heavy energy spell I would at the very least cast a circle. As I don’t do baneful work, I don’t have suggestions for how to protect you in that situation.
I do have protection sigils. items consecrated for protection, use protective runes in my home and wear on my person.
Whew I hope that wasn’t too overwhelming!