Axolotl Newbie Questions

Hi everyone! I've spent most of the day checking out the many many many different posts and articles shared here and I am so grateful that this site exists. I have a couple questions I can't quite find answers to though

We picked up a juvenile leucistic axolotl for our 40 gallon tank yesterday, he's about 4 1/2 inches long. Tank has fine black substrate, is filled all the way, screen top lid, no lights other than the room lighting.

My biggest concerns right now are that I was a bit misled by a friend of mine as well as by the associates at the store that we got the axie from. We are fish keepers, don't have any experience with caudates, and were told by a friend who has 5 axies and by the associates at the store that we didn't need a cycled tank to bring him home. But very soon after getting him home and into the tank I started reading more about water quality and realized that the cycle is more important than I was led to believe.

We do weekly water changes on all of the many tanks we have in the house, but I'm not sure how much and how often I should change his water until we get a cycle established. (10%, 25%, 50%?)(daily, every other day, weekly?) Willing to do whatever is needed to keep this sweet little guy happy and healthy.

Also wondering how much I should be feeding him of the bloodworms and blackworms we got. I used a pipette to give him blackworms this morning and got about 15-20 in there that he gobbled right up. Is this enough for each day, how big should he be before I start feeding earthworms?

Any insight would be greatly appreciated!

Thank you in advance!!!

Depending on how big he is, nightcrawlers are the best food.
THere is a subset among us here who never cycle tanks or check parameters. I do water changes on my tanks every two weeks, and more often if they look cloudy. I use water I age for a week and then maybe a little water from another tank or a handful of crushed leaves and that's that.

If you have cycled tanks available, I would take water from each of them and put it in his tank, plus any filter media you may have that is movable to help seed the new tank with good bacteria (doesn't have to go in an actual filter, you can just put it in the tank if needed). (This is assuming these are well-established tanks with no new stock that can be deemed safe and free of disease.) Watch your water parameters and do the same maintenance that you do on a new fish tank, bearing in mind that axies are "dirtier" than fish; kinda like really dirty goldfish. Technically, you don't "need" to have a cycled tank, but just like with fish, the more stable the environment, the better. I have learned that with my 40 gallon(not filled because it's too deep) with 2 7-8" axies, I needed to do about 75% water changes every other day to keep the ammonia down. I have a lot of fish experience, and without it, I think I would've been overwhelmed and worried about everything. If you can successfully keep fish going, you can keep axies happy and doing well. You already know the basics of keeping aquatic environments; you just need to learn the specifics of axolotls!
He is probably big enough for cut up nightcrawlers, or if you're like me and don't want to do that, he can eat smaller earthworms like mine do. I've heard that they sometimes don't like the taste of the cut up crawlers, so you need to soak them in water first.
If there aren't any hiding places, you need to add that. I have natural driftwood and hollow out the sand underneath but mine don't really hide often.
If by "fine substrate" you mean fine sand, that's great. If it's gravel, it's got to go! Anything in their tank needs to be digestible, small enough to pass all the way through the digestive tract, or too large to get in their mouth (meaning noticeably bigger than their head).