Exactly. That is a windshirt/jacket and should be ideal. The idea is that your windshirt goes on the outside most of the time. You can then add and remove insulation on top or below as needed. If it begins to rain lightly, the windshell will most often be enough to keep you perfectly dry. It is only when it starts to rain heavily that your rain shell comes out. The bonus to this system is that by adding a relatively cheap windshirt to your kit list, you greatly reduce the wear that your expensive rain shell will go through thus making it last longer. The consequence of this is that you can safely buy a lightweight rain shell and be confident that it will last you plenty long enough.
Before I started using a windshirt a few years ago, I seemed to be constantly having to add and remove insulation in order to keep my temperature regulated while hiking or cycling. It would go something like this: start with baselayer on its own until there was some wind making me cold, add a fleece. I would then soon after get too hot, remove fleece, get cold, add it again. Then it would start to lightly rain, so add rainshell, get too hot, remove fleece, stop raining, remove rainshell, get too cold, add fleece and so on. A freaking nightmare. The windshirt makes practically all of these wardrobe changes unnecessary. Additionally, like you said, you can wear both your windshirt and rainshell which will provide you with a bit more insulation than a heavy rainshell alone.
Anyways now for some suggestions. I want to be say quickly though that a 'lightweight rain shell" does not mean that it will be any less waterproof than a heavyweight eVent shell or goretex pro shell. The options I'm suggesting will protect you just as well from rain, and have comparable levels of breathability but will be less durable. This is because they are 2.5 layer as opposed to 3 layer jackets. The part which will likely wear out soonest is the breathable membrane part on the interior of a 2.5 layer jacket. In my experience this almost always comes under the manufacturers warranty when it wears out.
My top picks would be:
RAB Spark – This is the rain shell I use all the time. Uses pertex shield+ 2.5l. Two large chest pockets big enough for maps and gloves etc. Very good helmet compatible hood (useful for cycling). Is plenty durable. Uses 30d fabric. Weighs 9oz.
Montane air – A light, 3 layer eVent jacket. Uses 15d fabric. Really excellent helmet compatible hood. 10.9oz
Outdoor Research Helium II – Ultralight pertex shield+ 2.5l jacket. A great option, but bear in mind the hood is not that great as when fully tightened, it leaves a bit of the side of your face exposed (the reason I did not buy one). OR has one of the best warranties in the world. They will replace it for pretty much any reason. This means even if your dog chews it up, they will give you a new one. Uses 30d fabric. 6.4oz or probably less
Cheaper options are the Patagonia torrentshell which can be as low as $75 or the Marmot precip which can be $40.
Now to your question about fabrics. Just to put things into perspective, I have a goretex proshell jacket and a very good eVent jacket. I always leave them at home in favour of the much lighter spark. I would only ever take the others if I plan to be doing some serious climbing and constantly scratching up agains rocks etc. If I was going bike touring there is 0% chance I would take the much heavier gore and event options. If I had to put the heavy fabrics in order though I would say from best to worst for breathability and comfort (they are all as waterproof as they come) – eVent, polartec neoshell, goretex pro.
Hope this helps make your decision a bit easier.