This all boils down to knowing the requirements for what you're working on. Until you know exactly what you're going to be designing or fixing, and the requirements associated with it for its intended use cases, "generally" doesn't really apply. Why? Because, generally, as long as you operate within the limits of a component as given by the manufacturer's datasheet, then that's generally OK. However, that doesn't mean the device containing those components will operate as required.
For example, when you mention medical devices, do you have the specifications for those devices? Are there requirements for how accurate they need to be in order to be considering to be operating correctly? Are those devices going to be in an environment where they have to be operating to specific levels of accuracy? Do those devices have regulatory requirements in addition to any technical requirements?
Without knowing the product requirements, a $5 multimeter and some $3 wall-wart power supplies are accurate enough to make transistors, controllers, op amps, etc. operate. It's easy to get caught up in all the cool equipment and making all the displays match up, but unless you know that you need a certain level of accuracy or resolution, you probably don't need it (yet).
You've got some good gear already. Get started on what you want to build or fix. As you learn more and/or new requirements come about, you'll adjust what's in your lab accordingly.