i was only able to recover a fraction of my total btc i should have in my wallet.
I dumped all the private keys from all my received address' and sweeped them in Electrum
is it possible that more transactions will appear when the blockchain finishing syncing?
i have 3.3BTC in pending amount (correct perceived amount)
will I have to wait for the sync to be complete to know if my BTC is actually there?
You don't need to wait for any kind of sync in Electrum. And you probably forgot change addresses (shorena has that covered):
Completely forgot about the dumpwallet command