Wow, you have your hands full. 3 very different subjects and all with different PE techniques.
Gato - I would imagine you would want to fair in the PE to where it meets the plastic. In other words shave out about the thickness of the PE so it matches up cleanly against the remaining plastic on the hull. That would be for the hinge plates on the sides. That said pay attention to Eduard's instructions. This could create some issues on top that I haven't thought of. I haven't thought about the best adhesive to use. CA could be too messy. When it comes to PE I like adhesives that are more forgiving. White glue may be just the ticket. The nice thing is that if you don't like the result you can start over. The other nice thing is that you can mop up any extra glue without messing up your PE. Another possibility is to use Alene's Tacky Glue (basically a faster and stickyer white glue) to tack it in place and then go back and work CA in for added strength. I'd be interested to hear what you decide to do and how successful it turns out.
Missouri - That's a whole different animal. Lots of little stuff. I would suggest getting your hands on a good bending tool if you don't have one already. If you need more information on that let us know. Mission Models has one and The Small Shop has a product called the Hold and Fold which I prefer. You definately want to use white glue here. Elmers is the best. The advantage to white glue is that it shrinks, holds well, and as stated before can be mopped up for a nice clean finish. If you're concerned you can go back in and add thin CA for added strength. But it shouldn't be necessary. For the radar and such I highly recommend the Alene's Tacky Glue. The advantage is the same as white glue except that it grabs hold quicker than Elmers. I also recommend painting your PE before applying.
Panther G - Armor guys like solder. I use solder as well for certain things.
You'll know PE much better after these three projects! Let us know if you have any questions. There's certainly more detail to be shared than I've provided here.
Dave