well, you can use the market analysis to see, if the competition can fill up the route. however, this doesn't mean you will, as the competition might have a major network to feed the route.
personally, I strongly recommend not to start with cargo as it is way tougher than pax service unless you happen to be very familiar with it - which, with all due respect, you yourself mentioned not to be.
build a pax airline and if that works you can still found a cargo airline. if you need information on how to start in the first place, check this link: AS for beginners
Yeah, I can see that.... I did start a pax in the trial. After purchasing credits I decided to give cargo a try..... Manly to try and figure out game mechanics.
If it does not succeed, which may be the case, I will probably go back to pax again.
Gotta say this can be addictive.... Always wondering how it is doing.....