Buffett is managing Berkshire Hathaway, which manages other people's investments. If you believe in his strategy, buy into his fund, don't try to imitate him.
Not necessarily. Berkshire's stock price is based on how well other people think Buffett manages money. And his reputation is pretty darn good right now.
There've been times - like 1998 - when Berkshire stock was very much overvalued, and you'd be better off imitating Buffett than buying him. Hell, back then, Buffett thought Berkshire stock was overvalued, and got rid of $20B of it in buying General Re. If Berkshire is selling Berkshire stock, it's probably a good sign that you should be imitating and not buying in.
...however, I don't think now is one of those times.
Unfortunately you can't imitate him with high accuracy the way you could with an ETF since they have a number of wholly-owned subsidiaries. That's also what allows their stock to get out of alignment with market value of their holdings.
You can get a good idea of whether Buffett thinks Berkshire is undervalued or overvalued by whether he uses cash or stock for acquisitions, though. When the stock is overvalued, he'll trade overvalued Berkshire stock for undervalued other stocks. When the stock is undervalued or fairly-valued, he'll use cash for the purchase.
As Buffet has mentioned himself, Berkshire has a serious disadvantage compared to a small investor: tons of cash, meaning it only makes sense to make huge bets thus limiting its choices.
There've been times - like 1998 - when Berkshire stock was very much overvalued, and you'd be better off imitating Buffett than buying him. Hell, back then, Buffett thought Berkshire stock was overvalued, and got rid of $20B of it in buying General Re. If Berkshire is selling Berkshire stock, it's probably a good sign that you should be imitating and not buying in.
...however, I don't think now is one of those times.