Few beginner questions

I've decided to try keeping tiger salamanders since I've finally adopted out the last of my foster herps and want something new for myself(and that i get to pick out for once.) As it is i have experience with complex fish tanks, herps, aquatic frogs, and insects but never salamanders. So i got a few specific questions.

Feeding. I loathe crickets after having kept them for years and I know people use worms as a staple with sals. Where do you get your worms and what precautions do you take? I found super worms to be my favorite food insect to date but im not sure if their hard exoskeleton would be ok for the sals. I've also specifically raised them to pupae for an easier snack for a disabled gecko. I thought beetle pupae would be a good side source of variety since salamanders in the wild might come across them when eating?

Also with the worms, how do you keep them from burrowing into the soil? Or is it ok for a few live worms to be in the substrate?

Im having quite the time finding good soil. Is there any chains(walmart, lowes, etch) that carry a good brand ?

Finally, i keep finding mixed info on keeping multiple salamanders together. Most sources say they are solitary but can be kept in groups as long as they have space and are similar in size. My question is if it really is better off for them to just be alone. I have no interest in causing my pets stress for the sake of having more of them. My terrarium is 29 gals and i plan on doing 6-8" of soil.

For reference I have two adult tiger salamanders.

Food: I almost always feed my tigers only Canadian night crawlers that I get in refrigerated cartons from the Walmart fish bate section. One of my tigers once in a blue moon refuses the worms so I get some large crickets from PetCo.

Feeding: I hold the worm in front of their faces with my hand until they latch on. Once they grab a hold they very rarely drop it so I don't worry about them burrowing away.

Soil: Most larger pet stores have Coconut fiber (my brand of choice is Eco-Earth). I use only this because it is cheap, easy to find, and easy to care for.

Housing: Tigers are solitary. Except for getting excited during feeding time and mistaking the other's tail for a worm they don't notice each other's existence. (neither is hurt.) My two share a 20 long with no problem. I'm not sure what the dimensions are on a 29 but I feel like a third in mine would be very cramped.

Thanks for the response! The thing about soil is that i plan to keep some plants. However may just burry some small terracotta pots and plant in those for a nice effect. Still gotta find a small bag of soil but it should be cheaper.

A friend had an enclosure of soil with plants but got tired of maintaining whatever soil mixture she had in hers and went to the pot method you mentioned. I think she said it was cheaper with the coco fibers too if that is a worry. Whichever you do (you probably know this already), but make sure the soil your plants are potted in does not have fertilizer of any kind in it.