Got this feedback from Studio Tomahawk who I had emailed prior.
1. At what point in the turn sequence is the spotting check made?
There is no point when you make a spotting 'check". Basically, you check at any time which enemy is spotted and which aren't.
2. What stops a player from using a spotting check to measure range for shooting? Since cant measure for shooting before declaring.
Nothing. We usually allow pre measurements in our games.
3. Once a unit is spotted does it remain spotted for rest of game?
No, if he moves, if the weather condition changes due to random events, etc... he can move from "spotted" to "unspotted".
4. Does each unit need to spot each other until. As in if spotted once do all allies know where the spotted unit is?
Yes. A unit spotting an enemy doesn't mean that his allies will spot it too. Keep in mind that though our battlefields are usually quiet, in reality there was a lot of smoke, noise, etc... And they did not have any modern way of transmitting the informations.