There was an entire thread:
TL;DR:
Resources required increase slightly with each kingdom that is released (the pools that contain rares and commons are constantly expanding, so you’ll need more glory/gold keys with each new kingdom that is released), and it depends on what troop(s) are in the event pool and not in the general drop pool, but a safe estimate at the moment is:
~480 event keys
The bottleneck here is usually the kingdom quest epic, which you’ll need 12 extra copies of (given you finish the event and quest). If there is an epic available for glory during the kingdom’s event, it will be likely weighted 2:1 on event key drops meaning the quest epic is rarer, which is why you’ll need so many keys to just get 12 copies. If not, you’ll need 16 copies of the both epics, which will usually take about 420 event keys (your bottleneck will then be the non-quest epic, since both drop at the same rate and you’ll need 16 of it instead of 12). You can reduce these requirements slightly by opening gem or glory keys first, but you’ll likely need at least 300-350 regardless. In either case, unless the kingdom features two legendaries from the start, you should have the legendary at mythic before the epics. Ultra-rare drop rates are so common that you’ll have them all to mythic before any of the others you need.
~25k gold keys
(to max the commons and get about 50 of each rares) The number required increases for every common released in the future, including the ones released with the kingdom. By next kingdom release, it might be over 25k. Current estimates are in the 24k range, but kingdoms generally come with a couple new commons.
An additional ~6k glory keys or ~18k glory keys
The number required increases for every rare released in the future, including the ones that are released with the kingdom. You currently need about an additional 142 glory keys or 439 gold keys per 41 remaining copies of the rares. For each ~2.7k or so glory key you open before the event (again, this number increases with every epic released), you can cut your event key requirement by about 26 for a kingdom that begins with an non-epic event, or about 45 for a kingdom that begins with an epic event
x Gem or L5 Guild Keys
Spending gem keys at this point only slightly reduces your event key requirement and does nothing to lower your gold/glory key requirement and thus are generally better left for mythic hunting. You’ll currently need about 906 per new kingdom epic (increases every release, naturally), which will reduce your average event key requirements by the numbers stated above. Plus, this is an extremely unreliable acquisition method and more likely to net you a duplicate mythic instead.
I’ve stopped attempting to finish them right away altogether unless I can do it with event/gold keys alone because I don’t want to risk more dupe mythics from glory keys. If you get all the epics and above you need during the event, you can simply wait until the next mythic release to fill out your rares with Glory Keys at the cost of some efficiency and waiting a couple weeks, but if you use measured event key spending anticipating more of the epics and legendaries to drop later, glory keys are far too unreliable to fill in these gaps, meaning you’ll often be waiting an arbitrary amount of time (or until the next event) for your five star.