Your copy of the blockchain is YOUR copy. It doesn't do anyone else a bit of good whatsoever except insofar as there is additional redundancy, but that's a diminishing benefit.

An example might be in order. Say there was only one copy of Shakespeare's complete works in existence. The first duplicate creating some minimal amount of redundancy woult be incredibly valuable to have, so long as it was kept in a separate location. A third duplicate would make it even less likely that they would ever be destroyed, but it wouldn't be as valuable to society as that second copy was. By the time there are tens of thousands of copies of Shakespeare's complete works, the chance that all copies will be destroyed and forever lost are virtually zero, so the next copy that is added, while it technically helps ensure this is the case, it's really not measurably meaningful for anyone other than the person who owns that copy, because there may be tens of thousands like it, but that copy is THEIRS.

Same thing with Bitcoin nodes. Running a node does mean it is marginally harder for Bitcoin to ever be destroyed, but it's not like Bitcoin is meaningfully less resilient without your node.

Your node does relay pending transactions and newly found blocks to its peers, but they don't rely on your node alone for that information either. They would have just received it from a different peer instead.

Now, that doesn't mean running a node doesn't matter. It most certainly DOES! It's just that it primarily matters for YOU, and not anyone else. So long as there is reason for people to run a node for their own use, and it remains relatively easy to do so, node-count will continue to grow and Bitcoin will remain resilient.

If no one has any real reason to run a node for their own use, though, node-count will start to dwindle and Bitcoin will become less and less resilient, one node shutting down at a time.

Start9 and Umbrel are both incredibly easy to get started with. I would lean toward Start9, personally. I have used both and I like my Umbrel as a media and Nextcloud server, but my Start9 more as a Bitcoin node.

You're right. Turning off the internet every night is not ideal for your node. It means it will be required to catch up to the most recent block every morning before you can do anything with it. What is the reason you turn your internet off? Would it be something where you could just turn off the wifi and have your node hard-lined in?

Nodes are really quiet. Not like miners at all. Even in a small space, you likely won't notice any fan noise from your node.

Using a miner for heat is a good deal, if you are already using electric heat. You get KYC-free sats and heat out of the deal. I have done this with an S9 converted to a space heater. It is NOT an efficient miner, but you don't need it to be, because you'd be paying for that energy to heat your space anyway.

As for where to go to learn how to get this all up and running, nostr:npub1rxysxnjkhrmqd3ey73dp9n5y5yvyzcs64acc9g0k2epcpwwyya4spvhnp8 has videos on all of the above, from setting up your nostr:npub126ntw5mnermmj0znhjhgdk8lh2af72sm8qfzq48umdlnhaj9kuns3le9ll node, to connecting it to your wallet software of choice, to converting an S9 into a space heater, or just dabbling in mining using a Bitaxe connected to your own node for block templates. Ben breaks it all down and you will learn a TON about how Bitcoin works.