Hello, everyone
first of all i don't know how to create formulas in maths for every unit (attack and defence),
the only thing i noticed is that every new lvl of these units has the same amount of the previous and you can add something like (70% or 65% of 60 %) in order to take the exact number. But every unit is different both for gold and glass
so the only thing you can do without formulas is to make an assumption of these percentages, (for how much % you can add in every lvl)
if you have units the percentages for the first 10 lvls for the hoplite (offence )are:
lvl 4 - lvl 5 : 96.3% gold / 91.9 glass
lvl 5 - lvl 6 : 82.1% gold / 77.6 glass ( -14% / -14.3%)
lvl 6 - lvl 7 : 71.6% gold / 67.3 glass ( -10.5% / -10.3%)
lvl 7 - lvl 8 : 63.8% gold / 59.6 glass ( -7.8% / -7.7%)
lvl 8 - lvl 9 : 57.9% gold / 53.8 glass ( -5.9% / -5.8%)
lvl 9 - lvl 10 : 53.2% gold / 49.3 glass ( -4.7% / -4.5%)
and defence are:
lvl 4 - lvl 5 : 108.4% gold / 95.3 glass
lvl 5 - lvl 6 : 87.7% gold / 77.7 glass ( -20.7% / -17.6%)
lvl 6 - lvl 7 : 73.6% gold / 65.7 glass ( -14.1% / -12.0%)
lvl 7 - lvl 8 : 63.7% gold / 57.2 glass ( -9.9% / -8.5%)
lvl 8 - lvl 9 : 56.3% gold / 50.9 glass ( -7.4% / -6.3%)
lvl 9 - lvl 10 : 50.7% gold / 46.0 glass ( -5.6% / -4.9%)
lvl 10 - lvl 11 : 46.3% gold / 42.2 glass ( -4.4% / -3.8%)
so nothing its stable but you can understand that the percentage reduces for every next lvl
so make an assumption for the next lvls 12-20 lvls of percentages
for example you can go with: (defence gold)
12 lvl 42.6
13 lvl 39.4
14 lvl 36.6
15 lvl 34.1
16 lvl 31.8
17 lvl 29.7
18 lvl 27.8
19 lvl 26.0
20 lvl 24.3
and if you go there you can have a number for gold something like: 92,500,000 from lvl 4 to lvl 20 only for defence
i can't do for all units but as you understand it's only an assumption
the only thing you have to consider is that the units hit a max lvl (so check if they can get 20 lvl of upgrades)
you have 25 units and ships
3,000,000,000 i think is a good number for gold... so try to steal gold 
or create cities in glass
1,000,000,000 of glass its also a good number (because if you devide its something like 3 or 4 times bigger the amount of gold)
i have to make a propose: consider creating islands just for gold (make them rare) like one per 15 islands and a player can have only one city there
we have to mine gold somehow or mine something and create to gold ... so everyone can steal gold again or steal something like a bar of gold
anyway
all that for now ... i'm leveling up the palace (15lvl) and i can't go for the units upgrade till next year (as i did the presentation 2 months ago) so only assumptions
but i think if more people just sent the exact numbers of gold and glass per their lvl ... we will have a good estimation of what is happening there very soon
