Hiya!
Welcome welcome!!
So feeding: land hermits are funny. I tend to leave several kinds of food for them at all times. I remove mouldy foods & replace them with somryhing else.
Crabs take really, really small mouthfuls. They may be eating without appearing to disturb the food much, especially if they're still quite small. Secondly, they can seem picky. Their bodies tell them what kinds of nutrients they want at different times. Their physiological needs may vary depending on where they are in their moult cycle & what they've recently eaten. So sometimes they will like a kind of food, and some times they won't touch it. For this reason, providing a lot of variety is recommended.
In the wild, these guys eat almost anything - wood, poop, carion, plants, fruit.... because they've evolved to depend on a wide array of things we need to provide them with similar diversity. I'll link the nutrition page in case you hadn't seen it yet (it's a great read):
viewtopic.php?f=25&t=92554
Whether the hermit food you bought is healthy depends on the brand...
We tend to recommend that people avoid commercial crab foods due to preservatives and just crummy quality of ingredients. There's a page in the FAQ about commercial foods, I recommend you check it out.
I'll adress water next. If the bottled water is for human consumption, there is a high likelihood it contains chlorine/chloramines that can adversely affect your crabs.
A dechlorinator that says it removes chloramines, ammonia, & heavy metals is usually the best option. You just add it to tap water. It's also usually cheaper than buying water, so that's a nice advantage, too.
Seachem Prime is a popular brand choice, but there are other brands too... I wouldn't trust a hermit branded dechlorinator that didn't specifically say it treats chloramines, ammonia, & heavy metals. Hermit products tend to be overpriced & poor quality, unfortunately. Aquarium fish products are better, in general.
And salt water marketed for hermit crabs is generally of poor quality. What they need is a synthetic Marine Salt Water, designed for marine aquarium fish/coral keepers.
There's much more than just sodium in marine water, there's also magnesium, potassium, trace elements in itty bitty concentrations (that are still valuable to marine animals at exactly those itty bitty amounts)... so much stuff. And animals need that stuff.
Marine salt water shouldn't be confused with 'aquarium salt'... aquarium salt is just for treating sick freshwater fish.
Meanwhile, a lot of 'hermit crab salt water' isn't much more than a bit of sodium chloride desolved in water - it's better than nothing, but wont meet all of their physical needs in the long run. So what you want is something like Instant Ocean, a box of salt that you mix with dechlorinated water. This will help keep your hermits healthy!
On to bathing:
We recommend you don't. The reason is that hermits actually regulate their bodies using whats called shell water.... this is exactly what it sounds like - water stored in their shells. What's interesting is that it isn't just fresh or salt water inside the shell... rather they mix both to keep the salinity of this water at the same level as the salinity of their blood. This is part of how they maintain their bodies in tip top shape, even though they're basically marine animals that spend all their time on land. It's an impressive trick.
When you bathe crabs, you tend to risk upsetting this salinity balance. Crabs can bounce back from this, and can tolerate variation. But they are often stressed and weakened from the process of being captured & warehoused and transported, and they really don't need the extra stress of having to deal with the bathing.
Bathing is an old practise, developed before people really understood crabby needs. It's much better to offer salt & fresh pools deep enough for the crabs to submerge in. I like tupperware containers for this. You can add plastic aquarium plants egg cart, craft mesh, or build little shell or pebble staircases with silicone for them to climb out on. You have many options!
The bottom line is that crabs know their own needs best. Their internal regulation is best left to them. And I'll just add that while a crab running about energetically may seem to you or I like it's enjoying itself, this may in fact be a sign of stress in an animal that is often a preyed upon & will move quickly to try and escape birds or mamals that want a hermit snack!
I’m short on time right now but wanted to link you to the care guide. Happy Crabbing! 
Hope it helps with some ideas!!
