Basically, begin with a computer that has the number of processing cores of current premium computer offerings. Then choose an operating system that is a current offering on premium computers. Basically, begin with a premium-level computer.
Then reduce the number of re-boots for long computer life. And current computers seem to have very good sleep modes and very good stability for fewer necessary re-boots. However, a computer automatically jumping in and out of sleep mode can reduce the life of the computer monitor. So turn the monitor off when allowing the computer to sit in sleep mode.
Also, consider buying the computer from a computer maker and not from a retail store. A retail store can install their own configured version of the operating system on the computer. In that case a complete re-install of the OS from the recovery partition could possibly be a smaller OS install and a better performing OS.
The computer can have more than one operating system which is something to consider but the current method allows changing from one OS to another without a re-boot. That method is to complicated and risky to my thinking. Separate hard-drive partitions for different operating systems might be more stable but requires a re-boot to change between operating systems. But that's two operating systems on one hard-drive. I have previously had two hard-drives with a different operating system on each of the hard-drives. To re-boot to a different hard-drive required switching the wiring plugs inside the computer. Of course removable hard-drives are available. But a computer that is ordered with two internal hard-drives is basically just a system of file back-up and not two different operating systems.
As for a browser my current tip is that the computer might be more stable when the browser is configured to not allow motion detection by websites.