Hi Mooseadin.
You didn’t mention if you’d be open to transferring realm/rerolling, or what level of raiding you’re looking for, however, potentially we could be the type of guild you’re looking for.
I run a Horde guild on the joint realms of Lightbringer/Mazrigos. We are an 18+ social/casual raiding guild who raid in Normal and/or Heroic level raids twice a week - Wednesday/Friday at 9.30pm to midnight server time.
We have a wide mix of people with varying interests in and out of game. Most have busy real lives raising families, holding down jobs, studying etc.
In-game many are altaholics. Some raid regularly, some never, and some are somewhere in-between.
We have no restrictions on who can raid … if you have the gear for it, then it doesn’t matter how often you can sign up, or what rank you are … just add your name to any events you wish to attend.
We are looking for someone who would be happy to tank, but also is okay going in a different role when we already have enough signed - we generally follow a “first come, first served” rule on events … so the sooner you sign, the more likely you are to get your preferred role. Having said that … as mentioned before … plenty of people have alts and we usually have some who are willing to switch around when needed to accommodate as many as possible.
Effectively we have space for any role, because we can just shuffle around 
We are a casual raiding guild … we’re not planning on getting to the top of any league tables and we can’t guarantee getting Ahead of the Curve each raid, but we do have fun and we do, occasionally, kill a few bosses too 
We’re happy to have people along who have never raided before, or don’t have a lot of experience, and equally happy to have people who have loads of experience.
As for Classic … we are currently planning on trying to get a guild up once it comes out, in order for current guild members to have a home away from home. We don’t know how active it will be yet - it just depends on how well it holds attention from present-WoW. We’re currently waiting for confirmation on what realms will be available, so people can (hopefully) reserve character names on the correct realm prior to Classic launch.
If this sounds of interest, please check out our realm post, where there is further information, including how to apply: