Algae control - Lawnmower blennies are gret fish provided the tank is large and has sufficient algae growth. They will still need meaty items to eat though. if you had several large (at least 5-6 inch diameter) patches of bryopsis or similar algae, they would be a good addition. But too many starve because they are bought to control small bits of growth. They simply mow down the tall stuff, so there needs to be a lot. But like many blennies and dragonets, they also need a near constant supply of small food items. I'd call that a "maybe down the road" fish. But, I have heard wonderful things about the sea hares! And there is a blue and black one that is gorgeous!
Freshwater dip - Useful with many fish, but hardly a requirement. Also tricky. You have to carefully match temperature and ph. Don't do this unless you have read up a lot and are confident you can do it properly, or it'll cause more stress.
Glue - Once water is in the tank, silicone can no loner be used, as it secretes acetic acid (vinegar) while curing. Any good LFS
should have or be able to order an aquarium safe epoxy. Superglue is also safe to use with animals in the water.
Food - Both and more! Marine animals are used to having variety in their diets. I recommend Formula 1 and 2. Get ones as flake, one as pellets. Also, while feeding those daily, every few days treat them with about 1/4 cube of frozen Marine Cuisine. This stuff gets pricey in the long term, so for about $30, I made a year's worth of food. My ex girlfriend asked what I wanted her food processor for, and about two sentences into the explanation, she said "You know what, don't tell me. Just clean it before you return it, please."
I could have made the food cheaper, but I bought all my seafood from a pretty high end market. Those darn fish eat better than I do!
Also, for the foxface or any other herbivore, sheets of nori. You can buy this at the pet store in convenient small pieces for a "just for your pets!" premium price, or go to an asian market and buy it in large sheets far cheaper. Just be SURE to get unsalted, unseasoned. Have marine based algae products available for herbivores at all times so they can graze.
Good luck! This is where it starts getting really fun!!!