It seems like such a simple concept, but upon googling it's claimed by multiple sites that you need some sort of special API that fuse spigot + forge mod loader. The thing is, using the paid version of server.pro, I literally just had to upload a "forge.universal.jar" and a "craft.bukkit.jar" in the first file together of server files, and I loaded several mods with 6 plugins seemingly working perfectly. If it's as easy as that on a site like server.pro, why can't I do so without it?
Are you sure you got mods and plugins working on 1.8? All mod/plugin merging solutions (derivatives of MCPC/Cauldron) died messily in the 1.7.10 era.
Your description sounds like you put Forge and Spigot on the server and launched Forge. Which will make only mods working, without plugins.
For 1.8+ we only have the Sponge solution, which is not compatible with bukkit plugins.
Now that you say, I'm starting to feel doubtful of my memory. I know that plugins were definitely loaded, but I didn't exactly check if mods were running on the server. If it does happen to work, I'll send you screenshots of the server with mods + plugins (I can't check right now though, maybe sometime by tomorrow).