Word of advice

It's very hard for us to trust a closed-sourced wallet.

If it's not closed sourced do let us know, couldn't find it in the website

Otherwise everything looks great

Yes, all addresses are derived from one extended private key.

You can play around this tool to give you an idea:

I recommend you use BTCPayServer

Don't reuse addresses, it's bad practice. If you never reuse or consolidate, your chances of being blacklisted are very low

Honestly it's the only place I can check for news without getting high blood pressure from all the anxiety of clickbaity scary news.

If there is another outlet like SN please let me know

Sapiens Gut: Inside Story Never Finished The Cancer Code