E-Mount protect filters ...

An ND filter for long exposures, or a polarizer for anti glare are the only 2 filters I would think about and they are not suitable for protecting the front element of the lens as they are special effects filters. A lens cap does the protection. You will only degrade the photo if you use some sort of filter to (protect) the lens. There is some sort of IR filter to screw on if you want to do IR and use a tripod. I have 2 cheap bodies retrofitted with different IR filters inside the body which is different from screwing something on to the end of the lens.

I would suggest you not be too afraid of exposing your front lens element to nature (but) do use the lens cap to protect it.

As far as an ND filter (dark) filter, with the 2 lenses you have, you will want a 49mm thread. I don't have too much experience with ND even though I carry one (just in case). Again, you will want a 49mm one. They do make variable range, neutral density filters so you can dial in how slow you want to go (tripod needed).

JAW