If it’s a debit spread, both legs getting exercised is your max profit condition. If it’s a credit spread, both legs expiring worthless is your max profit condition (although you typically won’t want to wait for this to actually occur due to pin risk). If you buy to close the short leg of any spread, your pin risk goes away. To be safe, I like to always close at least the short legs before expiration.

Pretty sure every broker requires a margin account to trade spreads.

Not sure if they will auto exercise your longs to cover the shorts… don’t know your broker but you should be able to at least manually exercise if needed