Hey there! Welcome to Haiku!
First of all, as I am an end-user I’m unfortunately not able to answer some of your questions. Hopefully, a Haiku developer will help you out soon.
Haiku is based on BeOS, a defunct OS from the 90s. It’s not a Linux distribution and uses a different kernel built by the Haiku team. Haiku is much lighter than your average OS, with very low hardware requirements. Apps also don’t take up much space nor system resources. For example, @Zenja recently released Medo, a fully-featured 4K UHD video editor with multilingual support. On other platforms, the size of Medo would easily be over 100MB, but on Haiku Medo is a slim 1.44MB! Additionally, we have a porting team that has ported many popular open-source apps, such as LibreOffice, many KDE apps and much more. The downsides of Haiku, I would say, is that it is still in beta. This means there will still be bugs and rough edges. We encourage you to file any bugs you find at the Bug Tracker at dev.haiku-os.org
Additionally, our web browser, Web Positive, is fully functional but still has some issues rendering content. For most static webpages it will work fine, but if a website has interactive content (i.e. YouTube) there may be some issues with playing that content.
Finally, our developer team is a small, closely-knit team. Although development happens every day (you can find evidence of this on the “Source Activity” tracker on our homepage), major releases are not released as quickly as some of us would have hoped, due to our small developer team, who have to dedicate their efforts to multiple parts of the system. Nonetheless, our developers, many of whom have been with us for years now, are some of the most hardworking, friendly and polite people you will ever meet. They frequently hang out here on the forums, and you’ll see the “Developer” tag next to their usernames.
I would also like to mention that there are plenty of volunteer opportunities at Haiku. If you are interested, you can have a look at the following page:
On behalf of everyone here, I hope you enjoy Haiku! Please take the time to explore the OS and if you have any questions or problems, please don’t hesitate to ask here!