When should I start getting runes?

Once you can get Tier 3 runes you might want to start getting them (level 20), the main irritant with getting runes early is T1 and T2 runes are completely obsolete.

Since you're starting out - just focus on pretty basic, universal runes.

You really only need ~2 pages, 1 AD leaning 1 AP leaning, to not be at a disadvantage in the rune department. Anything beyond 2 pages: you really want to have a large champion pool prior to that. Fortunately most of the good purchases are the cheapest runes available. But all 30 still cost 8610 IP with 27x205 and 3x1025 , so you might want to start getting them now.

Well, they make a HUGE difference once you hit teir 3, so I'd start now.

Personally, I got the low-bie ones while still climbing. I know almost everyone says it's not worth it, but hey, Its a small advantage and It's not like they're very expensive. :P

Whenever you can get tier 3 runes, start buying runes. I would go with AD marks, Armor seals, MR glyphs, Mpen marks, AD quints, AP quints, and AP glyphs. That gives you all the runes you need for two generic runepages, one AP and one AD.

I actually don't have a problem with tier 2 runes... they are definitely for sure weaker and less variety, but they are very cheap. I bought armor and attack speed tier 2 quints for example, weaker sure but it lets me have a few various "complete pages" earlier.

I guess tho, since at first you have only 2 pages, you should get AD and M-PEN reds, armor yellows and flat MR blues, and attack speed and AP quints. start from there, this'll make a "adc" page and a "mage generic" page.

after that it depends on what your most frequent roles are. my most commonly used reds are: flat AD, m-pen, hybrid pen, armor pen, attack speed, flat armor. my most commonly used yellows are: armor, scaling health, flat health. I don't think I actually ever use anything else. for blues it is very diverse... flat MR, scaling MR (at first I had only three), flat and scaling CDR, (I only have 6 flat cdr tho, and only just this week got scaling 4-9), I have AP (at first only 3 and then only 6 but now all 9) I have 3 Attack speed blues which I use in two pages, does that cover them all? and then for quints. I have AS, AP, AD, Armor, Movement speed. I have one flat health I used for a bit but currently do not, and I want all three pen quint types but currently have no pen in my quints. I use the AD or AP instead, but the PEN for some champs are better. I'll probably get armor pen quints first, I dunno if I'll get the other pen quints tho until I complete all my other sets... I still need to get tier 3 armor and AS quints TBH xD

my advice is, check out sites to see what your favored champs use and plan out a "buy path" to get complete pages for those champs.

If you look at my account, those are usually the most common rune setups out there, The Ability Power and Attack Damage ADC/JG pages are the first two you should try to get. You can also swap out the AP Glyphs with Flat MR Glyphs.