For the first one, there are several ways, for example, you can ask them to re-type the passphrase in a box to confirm, or ask them to type words at random position, e.g. re-type the 4th, 15th, 19th word in the passphrase.
For the second one, it really depends on what application you are building, in general, if you need to save the account, then save the generated public address to your database should be fine.