Would you be interested in uploading your Interplanetary Vessel? It looks like you put a lot of work into designing it! It looks great! Anyways, I came across a thread here (LINK) that covers this question pretty well. It seems the consensus is constructing it at a minimus of 150 km for two reasons. First, you will be able to use 100x time warp. Secondly, according to people of that thread, if you orbit any lower, you run the risk of hitting the atmosphere during docking if you overshoot your target.