[CoupedUpSubie]

As far as interval goes, it really depends on the oil. If you use cheap gulf 0W-20 synthetic then 5,000 miles is all I would leave it in for. Go with Amsoil Signature Series and their filter and Amsoil will guarantee the oil for 15-25k miles depending on the vehicle. I will be doing a UOA on mine after around 7,500 miles pretty soon.

As far as if it is cheaper, only if you use the same quality of oil the dealer or shop uses. If you run royal purple or Amsoil then it will be more, but the oil will be of a higher quality.

Only use for a magnetic drain plug is pretty much for piston rings or cylinder walls. The rest of the metals produced by wear are non-ferrous, meaning they won't stick to a magnet.

If you have the space and want to change your own oil then get what you need and do it. Just be sure the filter old gasket comes off before you put the new filter on. If you don't it could be goodbye engine, and the dealer could say too bad, it's not covered because you screwed up.