Glad to have you here, Joan.
First of all you can't possibly go wrong with the 560.
AC:
We are in Olympia, WA with a similar climate. We have used the AC once, but were very glad to have it. Since you can't add it later, I think it's a good choice to do it now - when you do use it it will be a lifesaver.
Solar Hookup:
I would have done this option if it had been available when we purchased last year. However, you will still need to transport, setup and plug-in your panel every time you camp. With the 560 you may want to consider a permanent mount on the flat roof as I did. With my 85w panel electricity is almost never a factor for us anymore, and there is never any setup.
http://www.campinnforum.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=766&page=3
Sunroof: I'm glad we got it. You look up through it at the stars at night. With the 560 you can get both sunroof and fantastic fan. With a 550, where you can only get one, I would skip the sunroof and get the fantastic fan.
Backup Lights: We added them too. For the money, why not.
Fantastic Fan: Absolute necessity. Couldn't camp in the summer without it. The thermostat will kick it on and off during hot nights.
Internal Battery Isolator: Yes. You don't want to have to worry about your TV battery getting drained.
Electric Brakes: Although not required, we got them for the safety factor. We are also towing with a small Honda CR-V, so I'm sure it appreciates the extra help when stopping.
BUT, we didn't get the park break. For $900, I'd rather throw a chock under the wheel. It's not like the brake sets automatically - you have to throw a lever. Perhaps your money would be better spent on the furnace than the park brake.
Side Tent: Absolutely. Change in there while standing up, and also put a PETT toilet in there at night.
Spare Tire: Cary recommended that we just keep a can of Fix-a-Flat on hand. Much lighter (I was concerned about the total weight). We didn't get this.
Door Screens: We love these. They are so easy to open and close. There is nothing better than camping in warm weather with the sound of water coming through the screen door at night.
Galley Windscreens: Yes, get these.
Water Heater: We got it but haven't used it much yet. However, at IRG, there were at least of dozen of these, and all the wives swore by them. Sounds like a good reason to start using ours.
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Options you may want to consider:
Propane Furnace: Because we had the furnace, we were able to do a good bit of winter camping. Although we would have never considered camping in bad weather before, once we had our 560 we found that we could go away for a weekend rain or shine and have a great time. We used it all winter at least once a month. Wouldn't want to try it without the furnace, though...
Tables: I think you will want both stainless tables. One for cooking, washing dishes, etc... and the other to store the cooler or fridge on. Even if you decide not to get the tables, at least have them install the brackets for both tables. This way you can upgrade later and they will just snap into place without any drilling.
TV/DVD: While this doesn't get used hardly at all in the summer, we used it plently during the winter. It also doubles as a CD player.
Unless you are short, I would recommend the SUV package. This raises the height of the kitchen three inches. Without this I would also be hitting my head on the hatch overhead (I'm 5'11"). My wife is 5'9" and would be uncomfortable if the kitchen were any lower. However, if you are close to 5'6" or shorter perhaps you won't want this option.
Water tank level meter: This wasn't available last year, but it certainly would be convenient.
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In Summary, I'd recommend the following:
Lose the parking brake (not the trailer brakes) and the spare tire (unless weight is not a concern for you).
Add the tables for sure, and consider adding the heater. The DVD player would be the next thing I would seriously consider after that.
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I hope this was helpful. Please let us know what you end up doing!