HD58X can probably run fine from the laptop headphone jack. May depend on laptop model as well. I used to run it from office laptop headphone jack without problems and pretty loud enough, but eventually got the apple usb dongle for better audio quality. Rm55 only from apple store.

For HD6XX, still ok to use the apple dongle but usually people will recommend a proper desktop dac/amp. May need to experiment and discover your own preference along the way. Some may settle for budget amp, some may spend thousands on an amp.

Depends. If you feel the audio jack from your phone good enough, then no need. Iem usually easy to drive so dongle is not absolutely necessary.

If you're serious into audio quality , you should.
Check out the ibasso dc03 pro.
It's my end game dongle. No point spending more.

think of it this way, u will upgrade ur earphones, but dongle buy once enough d, can use for all future earphones upgrades.............