What is/are the best way(s) to begin integrating with the Bitcoin community?
You are doing it right now. The community is present on this forum. There are other channels, but as long, as you want to talk with users, and not with programmers, then this board is the way to go.
What is/are the best way(s) to rapidly decentralize it (by getting a lot of people to mine it) before listing it on exchanges?
Use Merged Mining. If mining your coin will require mining the original Bitcoin, then miners will have an incentive, to commit to your network, without any additional work.
before listing it on exchanges?
If you implement P2P market correctly, then you won't need exchanges. Because most of them are centralized, and it is better, if you can make trades directly from your wallet. You can read some code from version 0.1.0, to get an idea, how to start implementing it.
What is/are the best way(s) we go about engaging unaffiliated third-party developers?
Just write on technical board, with some details. Write about a particular feature: what is new, what it brings to the users, which you cannot see anywhere else, or what is done wrong somewhere else, and you can improve it. Just post technical questions, related to a particular thing, one at a time, and you will probably get some answers.
Unless it is done with the cooperation of Core devs it will be just another altcoin
If it will be just copy-pasted code (as it is done in 99% cases), then yes. But there are ways beyond that.
with all-new supply
Why you need any new coins at all, and not just pegging existing coins?
So we need to attend a Bitcoin Core developer meeting on IRC to make introductions?
I guess not. At the current stage, your idea will probably be rejected, unless it will be better explained in details somewhere.
Is there anything else I should do?
More details, more demos, more code samples, and things like that. Many people have many ideas, but sooner or later, if you want to create something serious, then you need to dig into details. And now, we only know about "all-new supply" (which is a bad idea, unless you have a good justification for it, like a new supply of non-monetary things, like domain names).
Not with market cap larger than Bitcoin
If you create completely new coins, you start from zero. If you have non-zero starting point, then it should be based on "something". Enormous Proof of Work? Wrapped fiat currencies? Existing signatures, used in a new way? If it is completely separated from everything we know, then why it should have any non-zero value, at the very beginning?
Every single mining company in the world is actually losing money.
So, why they are mining? For fun? As a charity? Are people that rich, so they can put their coins into fireplace? Do they need to report some losses to avoid taxes?
Satoshi Nakamoto didn’t end global poverty, war, diseases and insulate mankind from all future disasters and major catastrophes. This one does.
How? In the first place, not every human has a computer. Not every human can access the Internet. So, not every human can even use fiat currencies in their digital form, through online banking, not to mention Bitcoin. There are also places, where there is no electricity. So, how do you want to make it running, without any power supply? Because "global poverty" is a huge topic, including also those, who are tech-illiterate, and never used the Internet at all.