I tried to maximize my mapcontrol with extra engineers. Some pros always builds a jeep and I like being able to see alot of the map and the jeep helps with that.
I was gonna use the WSC but it never came to be
3 eng will help you to get mapcontrol, well you have to micro them and abuse them as much as you can.
A jeep will help you to deploy on the map thanks to the vision and to abuse light flanks.
Getting the 3 eng and jeep isn't good at all as you'll delay your supposed 'early game" infrantry dominance : the 3 rifles. You'll lose your extra territories as you won't have the rifles to defend them and your jeep won't be really usefull as it's supposed to support the rifles flanks, which you have delayed..
Going the 3 engs, necessary means that you want to use your capping advantage. So getting a wsc without even using it, is bad. Wsc isn't even a real teching choice as sniper can be killed by anything.
Getting the 3 eng means that you want to get early viable tech, as early BAR or early M8 ; tech that your ennemy will have to counter by investing into some buildings and units : early M8 => T2 gren pak, early bars => vet inf, vet sup, t3... That's it.