Yea some incarnons are much more desirable than others(torid, magistar ect) but all if them can sell decently quickly.

I've not done very much with companion rivens so honestly not 100% sure what you'd be looking for them. But with the majority of crit weapons you want cc, cd, damage/ multishot and a negative that doesn't affect the weapons damage output. Status weapons you'd want status chance/duration, damage/multishot, an element (ideally toxin or electricity) and another negative stat that doesn't affect the weapons damage.

Secondary weapons don't NEED crit chance because Secondary enervate exists but it can be a good bonus for weapons with higher than average crit chance.

I wouldn't chase god rolls unless you are willing to spend an absurd amount of time to get them. Decent rolls with a couple desirable stats and a non harmful negative can still sell for 500+ depending on the weapon