So you now have latest version of Electrum, your wallet is sync and you see your total amount of BTC - is that correct?
The only correct way to confirm that sending is working is to actually try send some coins and see is it working.
There was one problem before for some users when they are import private keys from MultiBit Classic to Electrum, and it happened to me. I import my private keys from MultiBit to Electrum, and at first everything seemed fine - but when I tried to make the first transaction Electrum is just freeze and stop to work. This has happened for the following reason:
This might happen if you are trying to spend a large number of transaction outputs (for example, if you have collected hundreds of donations from a Bitcoin faucet). When you send Bitcoins, Electrum looks for unspent coins that are in your wallet in order to create a new transaction. Unspent coins can have different values, much like physical coins and bills.
If this happens, you should consolidate your transaction inputs by sending smaller amounts of bitcoins to one of your wallet addresses; this would be the equivalent of exchanging a stack of nickels for a dollar bill.
I hope you do not have that problem, but some users who try to recover old wallets with a large number of transaction outputs may encounter this problem. However this was happening with versions under 3.0.0, so it is possible that something has changed in that regard.
http://docs.electrum.org/en/latest/faq.html