A CPA will be good for advising you on taxes and how to setup the taxation of your LLC, but a asset protection attorney would be best suited for creating the LLC. If you choose to create 1 LLC, you can do it in any state, but you have to pay the state you own houses in a foreign entity fee, which is usually the same price as starting an LLC in that state.
The benefit of just 1 LLC registered as a foreign entity in any state that you do business in is that it is much easier to manage, 1 bank account, 1 tax return, etc.
If you set up an LLC in each state you own property, it will realistically cost about the same and give more asset protection because litigation on 1 LLC won't affect the other. However, it is a little more time consuming to manage because you need individual accounts for each LLC.
You should hold as many properties in an individual LLC as you are comfortable with losing in a lawsuit.
Also, with an LLC, I prefer to do a manager-managed, with me as the manager. A manager is not the owner and therefor will not have litigation against him/her. However, a member will be open to litigation because they are the owner. Some states will disclose the members of a manager-managed, others will not. If you use a state that doesn't disclose the members of a manager-managed, I'd suggest that.
An LLC can be taxed in many different ways, as a simple sole proprietor, partnership, C-corp, or S-corp. A trusted CPA who knows real estate would be able to advise you on this.
The usual rule of thumb is for flipping, an S-corp.
For buy and hold, sole proprietor or partnership (if it is more than 1 member)