How many addresses can an Electrum Seed generate? If I generate too many, they go red for some reason. So what is the maximum amount of addresses that a seed can make?
You don't need to worry about red addresses. Just remember roughly how many of those there were if you ever send money to one of them.

There is no practical limit of how many addresses Electrum can generate from a seed. To figure out, how much money you have in your wallet, Electrum needs to sum up the funds in your addresses sequence – of which I just said that it doesn't have a practical limit in the number of its elements. This causes a problem: When should Electrum stop checking for more money further down the address sequence? The solution is to introduce a gap limit g.

When Electrum sums up the money in the addresses, it has a counter c which is incremented every time an address has no recorded transactions and set to 0 every time it does. If c > g, Electrum stops.

By default, g is set to 20 since Electrum 2.0. Addresses beyond the gap limit are red. If money is sent to one of them but never to the g addresses before them, Electrum will not look for it.

The gap limit also determines how many unused addresses you're shown if you don't generate new ones.