Founder stocks and Employee pool

1. Is it common to issue equity to CEO as Preferred stock but other co-founders as Common stock?
2. When setting up a 20% employee pool, it is common to have terms that the unissued equity will be issued back to the CEO only, not co-founders, not angel investor?
3. What are the advantages in setting up a employee pool, I knew some prefer not setting it up at all?

Thanks.

1. No; it doesn't even make sense to give the CEO preferred stock. The "preference" in preferred stock is usually a liquidation preference, giving the holder of the stock the right to get 100% of their investment back before anyone else takes a dime. This makes sense for an investor that has put in money. As the CEO has not put in money, it doesn't make sense. Of course, if the CEO is also an investor, they would have some preferred shares as a part of that investment. But founders stock and employee option stock is almost always common.
2. No. That's bizarre and sounds rather unfair, unless there are special circumstances which I don't understand in your particular case.
3. You set up an employee pool so that you can issue employee stock options. Because those options have value, you will be able to pay your employees less (all else being equal) and you will be able to attract the type of talent that wants the excitement of working at a startup with the possibility of a large payday if the company is acquired or goes public.

The pros and cons of the size of the employee option pool are rather subtle and are discussed in detail at VentureHacks. I won't go into the details here; suffice it to say that during a fundraising, the option pool comes entirely out of the common shareholders' stake, but if you have to enlarge the option pool later, it is dilutive to both the common and preferred. Therefore common shareholders prefer as small as possible of an option pool, thinking that if they need to enlarge it later, the preferred shareholders should pay up, while the preferred shareholders prefer as large an option pool as possible, knowing that they don't have to pay with equity now, but if anything is left over unissued in the option pool, they will benefit.

To answer your questions:

1. No.
2. No.
3. An employee pool is the only way to reduce their dilution as you get more rounds of funding.

If you are worried the CEO keeping a stake in the company, then you can add something to their employee contract that they get a certain percentage of the company. That way, the evaluations are worked our properly and the stock can be issued accordingly.