Hi. I have to give my personal opinion on the type of assets you said you wanted . Although the cartoonish style might seem easier to make is actually a lot harder than the style of age of empires 2 or 3. The cartoonish style requires an artist who can draw very well and it requires that the artists making it are consistent with the style ( this is good for a team of artists that have worked together for a while and can compliment each other) . The other style like age of empires 2 or 3 is much easier for the majority of artists that you will find in the community because it involves photo-manipulation rather than artist painting skills. I strongly recommend that you do not make the project cartoon style. If you do, contributing assets will become a bit problematic because the styles will not be consistent. I know cartoon looks nice but i can assure you the other style can look good as well.
is a great example of an age of mythology building that is not cartoonish but holds the fantasy style.
A comparison
This last one is much harder to do than the wonder from age of empires 3 or the town center from age of empires 2. The only advantage with the cartoonish one is that once you made the texture for one you can reuse it multiple times. For this particular project that is not an advantage because different artist will be making the assets separately.The style will not be consistent. Even for warcraft most assets were a mix of hand painted textures and photo-based textures. I’m warning you about this as soon as possible so you can get more assets for your project and do not limit yourself to only artist that are very committed and have a high level of experience. If you had a team of artist i would say go for hand painted textures. However many people who have offered to supply assets say that they will model them but not texture the assets. This is a major problem for hand painted textures. I’m just saying all of this before you invest your 60$ in a style that most community artists will not keep up with unless is paid. Remember if you buy those buildings you are pretty much forcing everyone who wants to contribute to follow that style which is a huge hindrance. I suggest you to not purchase those assets unless they are just placeholders. Also realistic textures can easily be given a more stylized look later on.