If I am planning on buying a house, who or what do I need besides a buyer's agent and pre-approval? What if I plan to purchase the home with cash? Will I need an attorney? And are all these things paid through the closing costs?

If you want to pay cash for the home you need to get a title company to handle your closing for you. And you will need to buy title insurance to be sure you will get a clean title. Why do you need a buyer's agent? Or do you mean real estate agent?

You can opt to use an attorney if you are purchasing a very expensive home, but it is not necessary. The title company can handle the closing for you. And yes, the closing costs will be listed on your closing statement but you may have to pay an attorney separately for his services.

Don't forget to get a good home inspector involved to make sure you don't have a lot of hidden damage or needed repairs as well on the property. Go over the home with a fine toothed comb on any discrepancy the home inspector finds and have the owner repair/replace items before you take possession. Have that written into your purchase contract as well to be on the safe side.

In many states there are no "title companies" but you will have to use a real estate attorney, which I advise, since the deed needs to be searched, contracts and new deeds reviewed.

Next a home inspector, but none that the real estate company recommends, in fact I tell them to try and find reasons for me not to buy the house, if they don't crawl in the cellar and crawl in the attic and if they don't have temp guns and more they don't need to be hired.

If buying on contract get title insurance. Buyers have made payments for years only to find that the seller did not have clear title - the risk is to the buyer until title is transferred. If you are paying all cash get Title insurance.
A title company will insure that you can get clear title. They will search for judgments against the buyer(s) and seller(s) and liens against the property, access and easements, water/mineral rights. Read your preliminary Title Report. The Escrow company will pro-rate taxes, insurance and record the title for you. The selling Real estate agent/or attorney in some states, will write The "Earnest money Agreement" or "contract of sale" should indicate sale price, earnest money, down payment, form and timing of payment(s) and time of transfer. This should be written to protect you and allow you to get your earnest mony back if you decide not to purchase. If the contract is unclear or can be read two ways, have it corrected before signing. Usually the title company/Escrow company holds your earnest money and interprets the contract.
Only Closing costs such as points/fees to bank, mortgage broker or lender can be avoided with a cash purchase. Other closing costs: Title fees, escrow fees, recording fees, County, city taxes pro-rated - are necessary. A lender would check to see if the home was in a flood zone - did you check? A lender would check to see if the home needed a pest and dryrot inspection. Was the home appraised to determine value? Did you require a home inspection? Where necessary permits obtained? Is there lead paint? Asbestos? Condition of roof, drainage, septic or sewer? Well? Water flow and potability. Details on foreclosed properties and its procedure should be considerate too.