Your tank is still really pretty young (a few weeks/months right...sorry, poor memory
) right? If so, nuisance algae normally comes with the territory in the beginning until the "good" algaes like coralline are able to take hold. One concern since you are trying to keep everything alive (I am the same way) is that you may get too many herbivores and then when your good algae outcompetes the nuisance you may have a shortage of food. Just a thought to consider, I have no idea how many snails you currently have but I would add in small groups rather than trying to conquer it at one time. Although, you will always have to scrub the glass.
You will hear a variety of good and bad stories about all colors of hermits, I have tried them all and there are rogues in each. There is no way to guarantee either way that snails will be slaughtered or not touched at all.....it is a big crap shoot. I now favor utilizing only different snail species, but that is just my personal choice. If you add extra shells, you might curb their house-hunting a little bit while getting to enjoy the dynamic they add to the tank.
A fighting conch does a fine job on the sandbed, I don't see the harm in adding one for something new. Good luck deciding, when all else fails flip a coin.