When cleaning your iPad or other Apple devices, you should follow Apple’s own guidance:
How to clean your Apple products - Apple Support
Use of other cleaners or techniques may damage the device - its screen, or its associated anti-reflection and/or the sacrificial oleophobic coatings. Screen-cleaning should only be attempted when absolutely necessary; over-cleaning will shorten the life of the screen coatings.
Use of a screen protector is largely personal choice - but there are considerations.
iPad screens are robust, but the anti-reflection treatment and oleophobic coating can be easily damaged by tiny grit/dust particles that are unavoidable in many environments. The oleophobic coating is a chemical sacrificial layer that will wear-out over time.
Your iPad screen is the single most expensive component of your iPad - whereas a screen protector is sacrificial layer that, if damaged, is easy and relatively cheap to replace.
Zagg and OtterBox are amongst the better manufacturers of tempered glass screen protectors - with good reputation.
Some users comment that a glass screen protector makes the screen slippery when using the Apple Pencil. The alternative is a matt/textured film screen protector - but these have three principal disadvantages.
1) The textured film reduces clarity and contrast
2) Accelerated wear of the Pencil tip, necessitating frequent tip replacement.
3) No impact protection