Once again - I'm still learning, one person advises you to do one thing, the next person will advise you something different... The person I bought my first miner from told me all 3 should be identical pool address but with worker names <name>.1, <name>.2, <name>.3 respectively!
I won't claim that I know better than whoever told you so, but use your common sense, when F2pool goes down for maintenance or DDOS attack or whatever reason, how will a different worker name make any difference when the whole pool is down? using the same pool on a different port as a back-up pool hardly makes sense, let alone using only a different user name.
If I remember correctly viaBTC have a very low payout threshold so it's pretty easy to withdraw 'dust'...
The minimum payout on Viabtc is 0.001, S17+ makes 0.000554
BTC a day as of today's difficulty, which means you need to mine for a total of 1.8 days or 43 hours on Viabtc in order to get to the minimum payout, based on your connectivity and F2pool stability it's almost impossible to get a total of 43 hours of mining on the back-up pool, it would take you years of mining, things will be better if you have more miners, but with difficulty rising you might not be able to withdrawal from Viabtc ever, so if you don't have another gear that uses viabtc as a primary pool, a solo pool as back up will be your best shot, it also helps with mining decentralization oneway or the other.
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Well done, I doubt there is an easier way to find the block, and for privacy reasons, one shouldn't be sharing the block number/share because that may expose some details about them, I now know the F2pool username for member danieleither

, so if he wants to keep that private, he should change it.