I rarely send transactions from it, but now I wold like to claim Bitcoin Cash and the first step is to send all bitcoins to a new wallet, as recommended. The problem is that I am very reluctant to send most of my BTC because of frequent confirmation problems. When I was migrating from the full Bitcoin client to Electrum (the blockchain size then was about 100GB and I decided that it was time to start using a lightweight client), I sent a transaction (fortunately with only part of my bitcoins) using the suggested fee. It never got a single confirmation. I waited about a week, then had to use some command line functions (I forgot the details) to make the client to forget about it (BTC did not return to the wallet automatically) and resend it.
It shouldn't happen. The only reason for it to happen is either the miners don't like you (unlikely) or you messed up the fee or the propagation was bad. If you ever face this problem again, PM me and I'll help, if you paid a fair amount of fee.
but Is there a way to determine how much is enough? Is the fee suggested by Electrum reliable? Can I rely upon the information provided at
https://bitcoinfees.21.co/?
The dynamic fee provided by Electrum is usually enough. I never had a problem with using it till now. The site does give fairly accurate information. Its important to note that your mileage may vary, depending on factors such as the amount of transactions sent from the time the previous block was mined and the next block.
No. The mempool size is not a fair representation of the actual network load. When blocks are found in succession, the client would display a very low fee since the mempool is quite empty.
Does it make sense to wait until the Segwit activation? I really do not want my coins to became stuck in an unconfirmed transaction for an indefinite amount of time.
No. Segwit guarantee low fee nor the time your transaction would get confirmed.