In Illinois you have to be done, Cali Im not sure. Cali's test is longer because of seismic if I understand correctly and has more education requirements to.

Check this site - ncarb requirements by state

Only some states currently allow you to take the ARE concurrently with IDP. Pretty sure Wisconsin allows it, but not sure about Illinois. Since that's where you plan to settle down I'd suggest getting your license through that state. So, when you complete IDP have your record transmitted to the state of IL, or whatever. You can take the IDP anywhere in the country, the exam is the same, but once you complete your license would be for the state which you choose originally.

california allows ARE to be taken concurrently with the IDP process. there's also CIDP in california

Since it all the same test, you should continue your application through the state you started in - they don't care where you take it, so long as you pass and fulfill any other state requirements. Afterwards, you used reciprocity through NCARB (wherein you pay them a good sum of money and then they print you an additional piece of paper) and fulfill any requirements stemming from reciprocity and viola, you are now licensed in not one, but two states!

You need to meet a particular state's requirements in order to get the clearance from NCARB to start scheduling your tests. But then, as I understand it, you're just taking tests until you have passed them all and submit your scores to your state board. The ARE is the ARE wherever you are taking it. A particular state doesn't enter into it.

Some states, like California, have supplemental requirements above and beyond the ARE. But I don't think that there are any special California versions of ARE sections. Reciprocity works because any architect in the country should be adequately versed in lateral forces, not just the ones in California.

There are situations in which the state does enter into things. It's true that the ARE is identical in every state - and that it doesn't matter what state is processing your records while you take it, or even what state you're physically in while you take it (meaning you can register through New Jersey and take every test in Idaho if you feel like it.)

But there are a couple exceptions to this: first, if you take the test through a state that allows early testing (before completion of IDP) there are a few states that will cause problems for you if you try to transfer your record there and then register through them. Oregon and Pennsylvania are two examples of this: if you take the ARE out of their required sequence with IDP by testing through Wisconsin, California, Texas, Vermont, etc. and then try to register in Oregon or Pennsylvania they'll say "sorry - you either need to re-test or get your initial license somewhere else and then apply for reciprocity."
Secondly: there are a couple of states that have residence requirements, and won't let people test through them if they don't live there.

Whatever you do, you should be aware that there's a difference between testing through one state and then transferring your record to another BEFORE getting your first license, and getting licensed in the first state and then applying for reciprocity in the second. In the latter scenario you would be paying for two application fees, two sets of annual dues, months of extra processing, and in many cases you'd also need to wait between the first and 2nd licenses while your application for NCARB Certification is in progress (you need an NCARB certificate to apply for reciprocity in many states, and you can't apply for that until after you're registered in at least one state. It costs $150 per year and takes 5 to 8 months on average to get.)