So I am nearing level 20 and have a fair amount of IP saved up. I want to know what, if any, are the best runes to buy that are not only best in slot (or close) but also serve a wide variety of champions?
I have read a few posts about this but they are all WAY out of date so I am looking for some up to date advice.
Help?
Goes on both pages: Armor Yellows MR Blues
For your AP Page: AP Quints Magic Penetration Reds
For your AD Page: AD Quints AD Reds
definetely armor yellows, dmg reds and mr blues, quints u do ap or dmg or AS
For those that apply, should I get scaling or flat?
flat armor yellows (seals) flat magic resist blues (glyphs) which can always be swapped for scaling magic resist or even scaling cooldown reduction
on an ad page, I prefer getting
armor pen reds (marks) if you play ad assassins or if you want to scale as a caster adc such as 
(here, take flat ad quints)
attack damage reds instead, if you play adc or juggernauts (here take attack speed quints)
on my ap page, I usually get
magic pen reds
ap quints if you usually go mid
magic pen quints if you usually go as a poke support like 
once you have every champion (plus a spare 6300 for a possible new champion) you can buy more rune pages for these setups^
here's a good reddit post with a chart for every page you'll ever want, but the above two should get you going: https://www.reddit.com/r/leagueoflegends/comments/268xzk/the_only_runes_pages_you_need/
What champion do you play the most?
I think I'll be maining 
Lux mid, or maybe a support like lux or 
morgana. Should I get runes more specialized for those two roles since I assume they will share some BiS runes?
In my opinion you should byt flat AD marks and armor seals first. Then magic resistance glyphs. Then everything else you deem worth.
Armor because overall are useful for any class ( from junglers to mages, to mitigate monster damage and mitigate minion aggro and jungler ganks ) and flat AD because it' s a core for many junglers, that rely A LOT on runes, it' s good for any laner because lets them last hit better ( and also harrass with the auto attack the enemy, don' t forget that ) and makes your supports more of a threat.
This just to say what i deem the most important ones, then there is a way to optimize everything. like, you would like to have magic penetration marks for your mages ( most of the times), or AP glyphs, or attack speed marks for your udyr jungle. I do not even mention Quintessences because those are another matter totally.
