How do you know if the idea is viable before outsourcing?

I know that many of you have developed software for sale on the market.

First off, I know nothing about programming so the questions I ask are out of ignorance.

I've tested a dozen CRMs over the years and haven't been able to find what I want.

I was sketching out on paper some ideas for what I would want in a software and it seems (in my mind) that it would be simple.

I'm thinking I'd like to put the project out there on elance or odesk to get it designed but the problem is I don't know how viable it is.

Yes, it looks simple to me but I don't want to post a project and screw up my ratings if the project isn't even doable, or is way too costly, in the first place.

Can anyone point me towards resources that show what developers can do to work with the google suite of products (calendar, contacts, etc.).

Also, can anyone tell me the advantages of having a downloadable piece of software vs a software that is accessed online. For that matter, how is a software hosted online? Do I have to have my own server?

In any case, excuse the ignorance, thanks for the help.