Hire an architect to draw a cohesive plan for you so your addition will not look like an addition. Or consult with a structural engineer for removing the load bearing walls the correct way.

Good advice. I don't want it to be a muddle which is what invariably happens when you have too many small projects without the big vision.

How much money should I set aside for this? Is there a rule of thumb like 10% or finished cost?

My husband is a residential architect. The architect is important to drawing up what you want. Your builder keeps the subs in line. Find a very good builder. Interview a lot of them; how long have they been in the area? Do they do remodels often? Who are their engineers, etc? Get names up front and research them. Ask local banks who they work with in the area they could recommend. The bank we got our loan at works with our builder and recommends him highly; other builders from past experience they would not recommend and would tell us if we were considering them.

We are currently building our second custom home and we took a lot of time finding a good builder in our area (he lives in the area, banks here, and has built a lot of custom homes). Talk to others who have used the same builder and look at all of his houses. The finish out will tell you the quality of his subs. How long does it take him to build a custom house or remodel? Good communication with the builder is so important. Will he be offended or defensive with questions? He should not. Will he be open to minor changes as you go along? There most usually will be a few items that have to be altered for whatever reason; he should not be opposed as long as it is quick and easy. It is also up to the homeowner to keep on top of the building process (visit the site daily; take pictures and note any discrepancies with your builder); know what you are supposed to get and question it right away if you see flaws before building has progressed too far beyond. Some architects will consult and job manage for additional fee based on time and expectations. Good luck.

@gacarnegie: First off: good on you for recognizing how easy it is to get over your head and that an Architect or experienced designer pro are there to provide you with the services you need. I wish more homeowners thought like you do! :-D

I'll speak for Architects, but an experienced home designer can do most of this for you as well.

My new selling quote for Architects is:
"A good Architect will help you understand all the sides of an issue enough for you to confidently make an informed decision about it yourself."

The other thing about an Architect is they are your advocate: you pay them to watch your back.

For you, it sounds like you could use some consultation hours to just gather all your ideas and have them organized, prioritized and maybe even refined. Many Architects will do this for you. Explain all the things you want to do and that you want a game plan on how to go about them all. It will be your "master plan". It would organize all your projects, maybe tag $ to them, or at least define what would need to be done to get $ on them.

Once you have that, and prioritize what you want to do first, an Architect can draft some schematic plans and if that's all a GC needs to build from, that may be all you need along with some involvement of the Architect to guide decisions so it's not just you trying to decipher what the GC is selling you on. If it's complex, you may need more involved drawings. Your Architect & GC can advise.

Fees are up to the Architect. If it's an involved job, it's not unreasonable to see 10% to even 20%+ fees for the really involved designs & projects. If it's a small job, and they do a schematic plan and then just hourly for visits or phone calls, it can be a lot less. The Architects need to be the ones to advise.

If you were in LA, I'd be happy to go over it with (and still can offer services from a distance, being licensed in CA) but your best bet is to find a local pro and work with them. Houzz has a great pro finder (use zip codes for proximity searches!) for that.

Good luck!

btw: check with Ironwood Builders here on Houzz. I think he's in Forestville and may know of good Architects or designers he's worked with in your area.

ReSquare, as do the others, offer sage wisdom about the process. I appreciate the magnamity of all parties previously commenting. I will perhaps be a bit more defensive of the design position. I will offer that the smaller projects are more demanding: i.e. they require real 'gray matter' to create the best solution, in terms of design and constructibility. Good and bad design, frankly, cost at a minimum, the same money--bad can cost far more, in terms of long term functionality and marketability of a poorly designed project. Yes, as ReSquare states, if Ironwood is in your locale, they have a great reputation from their presence within the purvey of their professional colleagues here on Houzz and their references, too. It is a hallmark of this site, that so many tout the benefits of our interaction with other professionals. I wish you the best with your project. Happy Houzzing.