I am the owner and only user of the computer. Does that mean I should run everything with root? Of course not. It’s simply better to start with little privileges and then elevate when needed. Using any additional privileges should be an intentional act. I also do it the other way: reduce my privileges via sudo -u nobody.
The root account shouldn't exist either. Having god accounts is a bad idea security wise. Instead everything should follow the principle of least privilege.
No, you should run every program with only the privileges it needs. The very concept of running your programs with all your privileges as a user by default is wrong-headed to begin with. To strain the "user" model you should have a distinct "user" for every single program which has only the resources and privileges needed by/allocated to that program. The actual user can allocate their resources to these "users" as needed. This is a fairly primitive version of the idea due to having to torture fundamentally incompatible insecure building blocks to fit, but points in the direction of the correct idea.