A hybrid inverter will accept the grid as the generator input and I don’t think you will need anything but a main breaker from the power company between you and the grid.
Something like this for the inverter and no it doesn’t have to be this big to have the same functionality but to take the grid direct you probably do need some size. I honestly haven’t seen anyone setup a system with storage and the grid because if would be insanely expensive here. We have too many grid fees setting a high fixed cost.
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Not here we only pay for what we use, no minimum fees. If you research this, there are a lot of people doing this, to use grid as a back up for off grid systems. That is why companies are making the simple transfer switches. They have been doing this in RVs for a while, but most are 50 amp with built in converter battery chargers.
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Do they hit you with time of day peak metering?
Thats when you would really want to use your own power.
Years back my Dad had an RV with a 50 amp transfer switch but as I recall it was 120 volt only and it had a big NH Onan in it ( burned a lot of propane )
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No peak time premium, straight 9 cents. That’s why I try to to costs down or it’s not worth doing it. I have always had back ups for energy, power needs. I never could go through life blindly relying on someone else for my needs, to me that is a dangerous way to live. My back-up transportation use to be horses 
, now it’s wood gas 
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