Install an Ethanol's Wither Storm Revamp of Immersion server through the Control Panel (Servers → Select your server → Game servers → Add Game Server → Ethanol's Wither Storm Revamp of Immersion)
I didn’t get how to get mods on a Forge Minecraft Server. But after I made a normal one I was shocked by how fast and consistent the server was. My friends always had 20 Ping consistent, even without the best internet. And it was also very easy to set up. For the Prices you can get very good servers.