First going to congratulate you in receive these many comments. It is on the other hand very daunting to read all of these comments and plan around what has been said. u/Technoguyfication has quite a nice overall post about this.

Just to summarize the recommendations whilst also add more to your plate. Here's comment 171! 😂

Server Software

Start with Paper, they have a lovely development team who pushes out updates daily for optimizations and performance. Many server owners use this Server Software in competition with Spigot. It is HIGHLY recommended to stray away from Vanilla versions for various reasons, especially Vanilla Bedrock Edition. As I've already seen, you've shifted your focus over to Java, which is a good choice. There is a lot of support for plugins and other helpful modifications.

Allowing other Clients (Java & Bedrock Users)

• Allowing Bedrock Users access to your server is slowly getting easier with a plugin such as GeyserMC. However, as many have mentioned Consoles have a limitation that prevents them from joining. BedrockConnect helps with accessibility for Xbox's and Switches but requires a DNS change. This may require some technical assistance/involvement. PS4 will require a LAN to be setup. Don't forget to use Floodgate to allow users to join without needing a Java Account associated with their Bedrock Account. Minecraft Education could be considered in GeyserReversion.

Version Support

The latest version of Minecraft has awesome additions for decorating blocks and other capabilities. Whether you choose 1.16.5 and support older versions using ProtocolSupport, or start with 1.12.2 and support newer versions of Minecraft using ViaVersion. It's all your choice.

Whitelist

I would always recommend setting up a whitelist for any private servers. This allows you to make sure only verified users are allowed on the server. This may be a slight pain managing 100 players, however, you may be able to offload this task to other platforms, such as Discord for authentication using DiscordSRV. An alternative route would be to using a Google Form.

Server Logs

Server Logs assist in checking what commands are being executed whilst you're not online, contains any errors, player join/leave events. You may view these in the logs/ folder.

Pre-generating your World

One of many server strains for the newer versions of Minecraft servers would be world generation. This has been evident in versions later than 1.12.2. I recommended Chunky with a decent radius from Spawn.

Recommended/Suggested Plugins

• CoreProtect - This is at minimum one of the first plugins, I highly suggest users of various levels of knowledge to download this plugin. It greatly helps in administrating what actions have occurred on your server. Whether it be reviewing chat messages, blocks that are broken, explosions, sign placement, etc. You'll know who has done what event.
• LuckPerms - Popular Permissions plugin, which allows you to limit access to certain commands, preferably administrative or cheat supportive. Do note, this may take some time to complete, but all plugin-based server owners who roll out to the public, use this type of system.
• WorldEdit/WorldGuard - Building Management and Region Protection. This may be of assistance in creating a starting building before release, but also protects regions from being destroyed or modified. This access is only given to Administrators.
• OpenInv & SuperVanish - These plugins allow you to access inventories while the player is offline and also allows you to hide from other players noticing you.