Address length - 8 B (max 20 chars in human-readable notation)
So there going to be 2
64 possible addresses? Isn't it too few? Let's imagine your currency won the widest possible adoption and everybody (7*10
9 users) on the planet uses it, and has private keys for 100 addresses (that's the minimum amount in bitcoin, actually we should consider much greater number). In that case, from each individual's point of view, collisions are still unlikely. But in general they are more than likely.
There are 2^256 possible addresses, the rest 192 bits are not used at the moment. In future we may decide to use next 64 bits to extend
visible part of an address, then all existing addresses that are 20 chars long now will become 40 chars long. Right now if someone finds an address with the same 64 bits they won't be able to send transactions.
Another question - why coins are going to be indivisible? If that's just UI limitation, how divisible they are going to be by protocol?
It's not very convenient to have a lot of decimal places in my opinion. The current version of the protocol supports only 2^32 numbers, but in the future it can be changed. Centralized exchanges can use fractional numbers to track user balances and round amounts upon withdrawal.