For almost all people, you want 20% down on your mortgage. How you get that 20% is debatable. Many, many people starting out begin with a small downpayment and a separate loan for the rest of that 20%. There is nothing wrong with that method, other than a bit higher interest rate for that second small loan.
The buyer's agent is certainly debatable. When it comes down to the negotiations, suppose the buyers and sellers are bickering over a couple hundred dollars. It is definitely in the seller's agent's best interest to get the deal done before he loses the business. Thus the seller's agent often will cut his/her own take a couple hundred dollars just to get the deal to close. But if the buyer has an agent, there just isn't room to do that. So yes, you may lose a couple hundred by using a buyer's agent.
However, a buyer's agent has many benefits. Often they are helpful in so many ways:
1) Can spot potential problems that you never thought about saving you thousands.
2) Can narrow down your search saving you countless hours (and time = money).
3) Can help you get good contracts in your favor including sneaky terms that you might not have thought about. For example, a coworker of mine is closing on a house in 2 days. His buyer's agent got in a clause that the seller has to fork over $750 for repairs and in subsequent edits added that ugly wallpaper is a necessary repair. The seller didn't realize that and its an instant and free $750 for my coworker to take down wallpaper.
4) Greatly removes the headaches of coming up with a contract. That alone is worth the possibility of losing a couple hundred on a deal.
If you don't like your buyer's agent, then dump him/her. No harm done at all.
I personally would find out what you are approved for and go significantly less than that. Suppose you are approved for $1500 a month payment. Get a house for $1250 a month in payments. Then you have plenty of money for emergencies, fun, minor remodeling work, or furniture. Don't keep back a ton of money for purchases since you will essentially be paying a 6%+ loan on this money when you could get furniture interest free for up to 2 years. 6% or 0%, 6% or 0%, you decide.