I think you should consult a professional with experience in 83(b) election and dealing with the problems associated with that. The cost of the mistake can be huge, and you better make sure everything is done properly.
For starters, I would look at the copy of the letter you sent to verify that you didn't write the year wrong. I know you checked it twice, ...
You can use 1040EZ.
If there were any difference between the purchase price and the fair market value (which there wasn't in your case), it would have been listed as income on your W-2, and you would report it as wages on your tax return, which can be done on 1040 or 1040A or 1040EZ. You have not sold anything, so there would not be "investment income" to ...
I was told by the lawyers there was no tax consequence because the two
numbers were the same.
That is correct.
However, a tax professional tells me that since the start-up stock was
"realized" there invokes a taxable event now.
That is correct.
I'm now led to believe I owe cap-gains tax on the entire 4 year vest
That is incorrect.
An 83(b) election generally doesn't apply to ISOs except when it comes to AMT or disqualifying sales. If you exercised at the time that you filed your 83(b) election you will have started the clock on long-term gains treatment for tax purposes as well as established the FMV of the stock based on the date.
For example -
You receive 1,000 shares at $10 and ...
In the question you cited, I assumed immediate exercise, that is why you understood that I was talking about 30 days after grant. I actually mentioned that assumption in the answer.
Sec. 83(b) doesn't apply to options, because options are not assets per se. It only applies to restricted stocks. So the 30 days start counting from the time you get the ...