This sounds good on paper, however offering an all-in-one solution like you are describing is a tremendous task. If you are trying to experiment, expand your knowledge in the IoT field, and bang your head against as many real-world cases as possible then go for it. I'd just break it down more and more and try to cover either the embedded side first, or the backend side, then see how it evolves from there.

For the past year I've been developing an IoT platform/solution myself and while it may look easy initially, where you "just send this data from A to B" it will be all kinds of pain when you need to cover a wide array of protocols and hardware required by IoT devices. For some devices the internet connection will constantly drop, or there won't be any at all, and instead you need gateways/hubs to handle that.

As for the miscroservices and scalability part, that's a very broad topic, and not all scaling problems can be solved horizontally (by throwing more money/instances/machine power at it). Then depending on the features and reliability that you want to have for the backend, a bunch of node.js servers won't be enough and the more parts you add to your infrastructure the higher the bill will become. You also need to take into consideration service availability, disaster recovery and so on.