I too am not sure why you are wanting to wash the fabric ... but if you want to, go ahead ... After all, if it's not washable, now there's a problem!!!
I wash all my fabric as soon as it comes in the house, and check that it is colour fast, or treat it as needed. That way I know it's ready to go when the time comes. As for ironing, that waits until it's needed, so that it's freshly pressed. Otherwise, I'm sure I'd be re-doing it then as well.
As for your query re starting a new scrappy thread? .... why? why not continue on with the same Scrappy Showcase?
And all this, is JIMHO!!!!