Fresh water sailing? Not so bad from a corrosion standpoint. I'm guessing you'll be using the
turnbuckles for the stays? If that is so, gust loading could exceed the working value of the aluminum turnbuckle followed by disaster.
I got my 22' swing keel boat free but it is best to invest in the proper hardware from a safety standpoint (possible demasting situation) and with respect to the cost of replacing a broken mast.
Turnbuckles are one of the cheaper items when it comes to hardware.
I should read more carefully- you did say for the sidestays. Sorry.