Simple: create a new identity to develop and the same identity to make it known in the community (thus join the community with a 2nd account) . Use your previous account in the community as before.
If you must, also use separate VPN to access these accounts to disallow identification via IP number comparisons.
Licencing a piece of code is as simple as that: just state that the code is under the license, and you're done. Usually it's a good idea to add author information, too. The whole point of the exercise is that any other person can unambiguously know the origin of the code and the license (thus permissions granted) for its usage. There is no formal requirement....
It's as simple as that. All you need to do is declare the license you are using and add a copy of that license to the source repository. Note that for most licenses, you'll also need to specify the copyright holder and the year the copyright took effect in the licsece's body.
The source that you are required to disclose according to the LGPL is not the project you forked from, but the source code of your package. And the LGPL defines source code as "the format that is preferred for making modifications".
Stating in your readme which package you forked from and what changes you made to it is not wrong, but it is not what ...
Yes, you can use.
If you are not using it at all, no, but as good practice you should refer your inspirations.
Also, I would like to highlight what you said about copying code, it's a tight line because you are getting inspired by that code. Just take caution about how you write the code, and don't fall in a copyright problem!
You could create a new identity for development and then, with your other identity inside the community, pretend that you just stumbled upon that open-source tool you created with the secret identity. That way, nobody has to know that you are the author of the tool, and you don't have to possibly violate community rules by having two accounts.
(since I don't ...