"At what point might we want a tax advisor?"
The obnoxious answer is: BEFORE you moved. Obviously, a bit late for that.
Remember, after you do something, it's too late to undo it. Before you do something, you have lots of choices. Your problem (and the problem of everyone doing an international move) is that you don't know what all the choices are, so you blunder about and only afterwards discover that had you only done X, Y, and Z before you moved, you would have saved $1l,000's of tax.
The nice answer:
After the fact, you can still get some good tax tips to save you money. However, you're mixing up tax advice and tax preparation.
Tax Prep: If you're company is paying for tax prep, go for it. Use a reputable dual qualified US/UK accountancy firm. Most companies hire one of the Big 4 companies. These companies do 1000's of returns just like yours, so you'll be getting quality tax work. They are woefully overworked this time of year, though, so you may not get quality or timely service. You will probably be filing on extension anyways (yes! you will! don't argue with the tax lady!), so don't fret about 15 Apr or speedy tax prep and just make sure the extension for your two states (WI and the other one) and the Federal are filed.
Tax Advice: When your company pays for tax prep, it doesn't always include tax advice. You may have to pay for a separate advisor - ask the tax preparer whether they can also provide advice on residency status, remittance taxation, and timing of options and shares. If they can't, hire a separate person for that (or keep looking til you find someone who can do both).
I hope this was helpful.