The highest team power possible is 4725
The highest power a hero has at max so far is 775, so a team of 5 775 heroes is 3875
Emblems max out at 20 and they each give a flat 5 power each, so that adds 100 power per hero to 875 and 875 x 5 = 4375
However when calculating total team power, you can’t just add all 5 hero powers because there is a value for each TROOP.
I found exactly what is used to get the additional power each troop adds to team power, it is:
So a 4* level 8 troop = +48, a 1* 1 is +11, a 3* 3 is +33, etc…
(for reference see CP Calculation thread)
4* troops can go to level 30, so 40+30=70, 70x5=350, 4375+350=4725 which is the highest possible power a team can have.
However the most emblems I have seen on a 5* is 7. This is due to emblems only coming out 6 months ago and needing 1500 emblems to get a hero to 4/80+20 (thats a lot, considering its only like 505 emblems to max a 4* and 233 to max a 3*).
Also, most 5* heroes are lower in power than 775 at max, which are the last round of season 2 heroes like Poseidon. The lowest power a 5* has at max are from the classic heroes which at lowest is 752.