The only exchange that I ever use to swap coins (not switch to or from fiat) is shapeshift.io - they don't require user sign ups and you don't even have to keep your coin on a wallet they control. That's the biggest selling point for me, having had friends who lost big when exchanges went under. They also will refund your coin if you give a refund address in the event that the transaction is broadcast too late (don't use coinbase - it broadcasts too slow).
They do list Siacoin, but coins in high demand are frequently unavailable for a while. Personally, I plan to buy Siacoin, but won't before the wallet is done synchronizing - if it EVER finishes synchronizing (seriously, the absolute slowest blockchain download ever)
As far as mining goes, there are two ways to mine apparently. GPU mining works without any upfront coins held - for the moment - but as soon as people start turning on their Antminer A3 units the mining reward will crash. At the present rate, with an overclocked water cooled Nvidia GeForce 1080 Ti I get aroud 1 Siacoin an hour and I need a minimum of 500 to get a payout. The second way to mine, annoyingly, requires that I have 2000 siacoins already AND the wallet has to be done synchronizing to get the coin into the wallet. However, that will likely be the only profitable way to mine on a computer with the Antminers are loose.
My concern there would be if the 2000 coin requirement will remain if the price explodes. Similar to Dashcoin supernodes that require you to hold coins, there's no way for me to get into that without like a million dollars to drop so unless they plan to adjust that with the price it will become a growing barrier to entry.
