How do I go about getting a suppressor and how much should I expect to pay?
See the earlier post regarding what you need to determine first. For a .223 suppressor, prices can run from $475 to $1300 (not including the $200 transfer tax) depending on what you want.
What is the difference between the various sound suppressors and which one do you recommend?
Astonishingly enough, there isn't a lot of difference sound-wise between the various suppressors. Most suppressors will quiet an AR15 down to about what an unsuppressed .22LR sounds like. A $475 suppressor isn't that much different from a $1300 suppressor sound-wise usually (though you can probably tell the difference).
Where the difference in cost lies is mostly in compactness, weight, mounting system, ability to handle semi-auto or full-auto fire, shift in zero, ease of suppressor maintenance and durability. Decide which of these parameters you need and the choice of suppressors will narrow down quickly.
Do suppressors ever wear out?
Yes, like any mechanical item, a suppressor has a finite life; but they do last awhile. As an example, my Ops Inc. 16th Model is warrantied for at least 30,000 rounds, which is better than many barrels will do.
Also, can the muzzle brake that is currently on my rifle simple be removed and replaced by a suppressor? I think my brake is detachable. Thanks.
If the brake is attached via standard 1/2x28 tpi threading, then it should be no problem to find a suppressor that will attach using that threading. One problem that does occur though is that you are now attaching a 7"/20oz item to threads designed for a 1"/2oz. item. Many people do it and have no problems; but it probably isn't a great solution if you plan hard use for the rifle. The nice thing about this is that you don't need proprietary mounts for every rifle that will use the suppressor and the price of the suppressor is lower.
What are the pros and cons to registering a suppressor through a corporation vs. a personal living trust?
A corporation is perpetual. It lasts as long as the paperwork is filed and taxes are paid. Also any officer of the corporation may have access to NFA items (provided they could legally own them). A trust is cheaper to start and easier to maintain (no annual paperwork or taxes and in many states no filing fees); but it isn't perpetual and only one person may control the NFA item.
What happens if the corporation is sold or closed? The suppressor then needs to be transferred personally or to a personal living trust?
Considering that corporate law mostly depends on the state of incorporation and given the stakes involved, this is the type of question you really need to discuss with a lawyer. You can get answers on the Internet; but it won't be the guy giving you bad advice who goes to jail.
By the way, is there any drawback to getting a .223 suppressor for an AR and bolt rifle and also using it on a .22LR rifle and Ruger MKII? Is that possible?
A .223 suppressor could theoretically be used on a Ruger MkII; but you have to realize that most .223 suppressors are in the 7"/22oz range and are going to be very awkward on the barrel of a Ruger MkII. I haven't used a .223 suppressor with a .22LR but I've chatted with guys who have. They say it works well for the most part but that lead from the .22LR ammo can build up inside the suppressor and cause issues.