In high five i used to be able to hide the nevits blessing window through commenting out all the related code in the source. Maybe its possible that way too.
L2JMobius is overall the most functional. At least all the basics work but the support isnt the best for free users. You will have to do the heavy lifting on your own. If you ask for help on their forums all you gonna get is subscribers telling you to buy the subscription for better support and things like that. I have no experience with Lucera so i cant comment on it and with Acis the free sources are very old and the next update is years away afaik.
I hope you have success with your business but you chose the wrong place to advertise it, with a few exceptions this forum is full of knowitalls, narcissists and selfish users. Especially those that have some reputation within the l2 server scene. Not sure who you are tying to recruit here.
I remember it, well mostly that it was x2000 and had max enchant +15 which was the only server that did that before L2Gang (i mean low enchant limits and no red weapons). I also remember the squash fruit farming monsters, thats about it.
I used to run 400-600 players on a hetzner athlon server with 2gb ram back in the day and i used some really shitty scripts like rin4's buffer with memory leaks. Im only going to take seriously anyone that actually runs a server with these numbers when they tell you a vps isnt enough. The average vps CPU today is way better than an athlon from the late 2000s.
Try first with a decent vps and if you see it cant handle things have a plan to swap into a dedicated if you have to.
One thing i learned is that most players dont care about how the website looks as long as it works. Having a nice looking and modern website helps but not as much as you think.
I agree with everything you say about java but not with the crashing. Unless the pack is completely shit, filled with memory leaks, and unclosed connections, crashes are rare if non existent on a clean source.