I'm considering purchasing a second hand 40gallon with stand and hood, light etc... But it was previously used as a saltwater tank. I have goldies. Is is safe to do this?

If so, what should I do to prepare it?
How long before cycling and is ok to put fishers in there?
Any other guidance or experience in this will be helpful.
Thanks again!

I have had 2 tanks that were previously used. And one of them I do not know what they put in it (but I do know it was fish).

I cleaned it with water and bleach. I let it so for a day. Then I filled it up again and let it sit for another day. I did this until I got the bleach smell out.

You shouldn't have any problem setting up a fresh tank in a previous salt tank. Just wash, scrape, scrub off the salt build up from the tank, lights, etc.
There's no need to worry about parasites or diseases because of the osmotic differences between salt and fresh, your main concern will be making sure nothing is corroded (everything works like it should, the tank doesn't leak) and getting the excess salt off the tank.

As for cycling, the length it takes to complete depends, there's no pat answer. Temp., pH, available bacteria culture all effect the cycle time.

You can cycle a tank with fish yes but IMO unless you are willing to do frequent large water changes (which slow down the cycle time) then it is really easy to do a fishless cycle. There's alot of great info already posted about how to do this.

Best of luck.