As others have expressed- were already there. Understand though that the reason this hasn't caught on mainstream is the entire purpose of what you are asking is simple: it runs counter to the standards of commercial capitalism. We are talking about efficiency, self hosting, doing more with less, and cutting strings.
That said- understand that what you are undertaking is not dissimilar from building infrastructure in a company. You are building and expanding to meet your needs. Your needs are unique so there isn't a 'turn key' solution that will fit perfectly... so you need to try things and see what works.
As far as things you are talking about specifically: you are going to ultimately be dipping your toes into the virtualization world... so xcp-ng and proxmox are good choices. If you can get your hands on older copies and uh... source a key or two: esxi is also very beginner friendly but won't be able to upgrade thanks to their new pricing model. You seem like you are aware of the YouTube sphere so let me recommend 2GuysTech and the series on different hypervisors.
Once you decide on a hypervisor it's as 'simple' as building a PC to meet your needs. If you have one already I'd start there to get a feel for how much you can pull out of it to determine how much you may need. You can probably split up a single GPU or just pass it through (cost vs performance.). LLMs are power / resource hungry so that may require it's own GPU.
If power is cheap by you you can look into older server hardware but honestly this can be a messy space to dabble in (noise, heat, power costs.)
From there play with services that fit your needs.
It's very doable and there are some easier paths to take... certainly- but again the thing about homelabs is it's very custom. This is why the community (in general) is willing to help. We all have had to forge the same path.