Use f-air to approach as much as you like, as long as it's working. Just note that hitting a shield with F-air is inviting punishment, even if you pull back and attempt to land with an 'auto-cancel'.
It's up to your opponent to punish, though. If you've got an opponent who drops his shield after the first of three hits and takes damage from the F-air, you've got it easy. If you've got an opponent who keeps up the shield for all three hits but you pull away and don't get punished, that's nice. If you've got an opponent who punishes you out of shield each and every time, rethink using F-air in this way.
Look at the different ways of using F-airs. Short Hopped F-airs are good against taller characters, but leave you open afterward. Full Jumped F-airs are better against characters in the air due to its height, harder to hit grounded/small opponents, but don't leave as vulnerable afterward. Also look at which kick you're using, the first and second kick vary from the third which is stronger. Each kick can be used for a different tactic.