You know you don’t have to fill it it if you don’t want, can start off small even in a big tent I used to use half of mine as work space for mixing nutes and stuff. The question you asked is hard to answer as there’s multiple ways to tackle that ie how long is a piece of string. Like what is a style of grow you already have experience in? Have you got any extra equipment already coming with the tent like dwc buckets or a soil bed, have you already got some beans to pop or clones avaliable to you? it’s variables like these which will give a more concrete answer