I don't see a question to be answered in your first bullet. Are you asking if you should insure your consulting business? $1500 seems kind of high but depending on the work you do it could be competitive.
Regarding the rental properties, you'll have a hard time finding a competitive product that covers both properties with one policy (for physical losses to the property itself).
Also, when you use the word umbrella, keep in mind that an "Umbrella" is the actual name for an actual insurance produce that provides excess liability coverage (personal or business depending on the type of policy) if your underlying limits are exhausted following a loss. A personal umbrella, for example, provides excess liability coverage in case your personal auto or personal home liability coverage provided by those policies are not enough. Personal umbrellas can be had for very cheap for many millions in coverage. We have one.
Keep in mind that any insurance product is just a transfer of risk (you lose a small amount each month to avoid the risk of losing a ton of money very quickly). How much do you have in savings? How likely are you to find yourself in an extreme situation where millions of dollars are at stake? Probably slim, but only you can decide if you have enough. In your case, you may benefit from finding an independent broker that can look at your big picture (in fact, show them your diagram), and see what they suggest. If you're sticking to only quotes from big companies you may find that the call center person's knowledge may be limited to personal only or business only and that's it.