The advantage of clipless is a secure foot/pedal relationship without the binding or toe pinching that clips and straps can cause. Double sided clipless pedals are also marginally faster to enter, and (once you get used to them) quick and cleaner to disengage.

Most mountain bikers use Shimano system pedals and cleats, which is a defacto Mtb standard.

The drawback is that you need dedicated shoes, so it's not ideal for utility biking where you'll be doing lots of walking. (I use clips/straps and wear loafers for the commute for this reason).

As for shoes, like with any other shoes, fit is trumps, everything else is a distant barely important second.

So the decisions are easy. Pedals acording to budget, shoes according to fit, both using the same cleat system.