No there is no signup fee (but your firt bill will be higher due to paying 1 month in advance plus partial charges for the previous days when you initial signed up (it's just your plan but pro-rated for the time you were actually a customer).
An SD card is a memory card only. If your device could use one then you would need to buy that on your own.
However I think you are referring to a sim card which is used to connect your account to the network. If you are buying a Koodo phone then the sim card is free. If you are bringing your own phone then it is $10 for a monthly account (postpaid) and $20 fore prepaid (comes with a $20 prepaid credit upon activation).
Yes it is ok if you have a phone already. But make sure it works on Koodo's network and that it is carrier unlocked so that it can be used with other providers. On a monthly postpaid plan you also qualify for 10% off your monthly plan if you have no tab because you bring your own phone (you have to call in to have that added)