So i will answear some of those and i might cover some of your topics since i have some free time to spare.
-Only 1 kind of protection? For example, a protection like SmartGuard covers everything?
1. SmartGuard, AAC, and similar BOT protection systems aredesigned to detect and prevent the use of third-party bot software by players. They are not server protections against malicious attacks on your server. These systems work by monitoring and collecting data to identify and block bot programs used by players. Their main purpose is to prevent players from farming 24h/7 and destryoing the server's gameplay and economy. No other protection rather than that.
-I need to add protections, adverts, topsites and so on.
-Where can I find good protection?
2. When it comes to protecting your server against various attacks, such as DDoS attacks and SQL injections, it's important for server administrator (YOU ) to acquire knowledge and implement security measures. These measures may include setting up firewalls, implementing detection systems, regularly updating server software, and following secure coding practices for any websites or applications connected to your server's database. While some VPS or server providers may offer built-in firewall solutions, but are not enough.
3. You can run your l2j emulator to any rented vps or bare metal server outhere. I dont recomend to go big and rent a big ass server with 32gb of ram and 32 core cpu since you will waste your money. Personally i prefer to go with cloud services since are pretty cheap and scalable if you need more without having to re install everything from the start. Some of those are hetzer , OVH and Linode (linode not offer windows server option). A vps with 8gb of ram and 4 vcpu is enough to run a good amount of players. Ofc there are other things you need to considered once you go bigger and bigger or what functions your l2j emulator has. For example if you want to run phantom bot engine with 1000 fake players you might need more resources.
To conclude, before considering opening your project, set clear goals for the project. If you intend to scale it up, read up as much as you can. Otherwise, go ahead and open it, and solutions will occur as you encounter problems.
Some self-explanatory guides can be found here:
Follow these series, and they will cover many of your questions. Additionally, if you don't understand some concepts, try Googling them.