It may help to separate your issues into sections for the conversation with your agent.
Dwelling coverage - insurance companies insure for replacement cost, not market value, of your house (and not the land). Ask your agent to walk you through the program they use to calculate replacement cost. Make sure all the information in the program (e.g. square feet of rooms, number of bathroom, construction) is correct. Replacement cost coverage for your contents is generally 60% of the dwelling coverage. That number can be increased for a premium.
Flood coverage - It looks like you have a good understanding of it. I can’t remember if the dwelling coverage is replacement or depreciated. Ask your agent.
Auto Physical Damage - if you have older cars, talk to your agent about dropping collision. I really wouldn’t drop comprehensive because it’s inexpensive and covers a myriad of losses (some fool slicing your tires, hail damage - non-collision types of losses). I also wouldn’t consider a comprehensive deductible more than $100. Ask your agent to quote you $100 and $250 deductibles and you’ll see why. The difference is minimal. Auto physical damage is based on market value of the car at the time and place of loss. Your car is always worth less than you think it is in case of a total loss. That’s why it’s important to purchase Gap insurance if you have a loan on a new car.
Liability. Liability is the most important part of any insurance policy. It protects you in case of a situation in which you are legally liable for a loss to property or person. On the auto policy, the people who go for the state minimum on their car insurance find out that it’s just not enough coverage in case of an accident. You can be successfully sued for any damages over and above your liability limits. You have liability coverage under your homeowner’s policy to protect you in case someone is hurt on your property. It’s just not worth risking your financial future to save a few dollars. Liability is the cheapest part of your auto policy if you have a good claims and driving record. I’d rather you drop comp and collision and raise your liability limits if you have to make a decision based on cost. The absolute minimum you should have on your auto liability is 300/500/100 and $300,000 on your homeowner's policy. You should also have MedPay and PIP to cover you and passengers in your car in case of an accident regardless of fault. MedPay is really cheap.
Umbrella. This is always a balancing act. The old rule of thumb was to have liability coverage three times your annual income. That’s pretty much out the window. It needs to be enough to protect you financially. The homeowner’s and auto liability are primary; the umbrella sits on top of them. If you have 300/500/100 on your auto and 300,000 on your homeowner’s plus a $1mil umbrella policy, you have $1.3mil coverage. The umbrella goes a bit further on giving your coverages not in your auto or homeowner’s policies so you need to have a clear understanding of what it does for you. One thing you might want to ask your agent is to see if you can have $1mil on the underlying coverages and that may give you enough of a comfort zone to drop the umbrella. Raising the underlying liability coverages is so inexpensive I’m surprised most people don’t do it. Again it depends on your claims and driving record.
I cannot emphasize enough that having high limits of liability is the key to protecting your financial future whether it be in the underlying policies or with an umbrella. Also, make sure your dwellings are adequately insured for replacement coverage and you understand the deductibles (windstorm usually has a huge deductible). You don't want to have a house fire, a tornado flatten it, or some other type of catastrophic loss and find out you were not adequately covered.
I hope this helps.