Survival is 1.12, which is the most preferable version to use, but 1.13 does also work.
'Sorry totally confused returning player' - No problem at all, if you have any more questions feel free to ask below or PM me on discord at Sunset#3438. You can also ask in-game through ./helpop or in the #help channel on our community discord.
The mod packs used on other servers (like Tekkit) are just collections of mods. Manacube doesn't use a pack per se, but does use a bunch of mods. Most are the same across games (Survival, Skyblock, etc.) but there are some differences.