There are several answers to your multi-part questions in my humble opinion:
Commissions: NEGOTIABLE BY LAW, although some Agents/Agencies have a bottom that they will not fall below, it is between the property owner and the Broker what commission and what services are offered.
Marketing; GENERALLY speaking, when you sign an exclusive right to sell agreement you are agreeing to allow the agent to market your property in whatever fashion way they see fit as long as it follows all fair housing laws. If there is a particular marketing method you very specifically don't want, tell them.
Length of Agreement: That all depends. Often sellers think the shorter the agreement the harder the agent will work; this is not always the case. An agent needs time to get the listing out there, market it, re-market it, follow up, etc., too short of an agreement an agent might give up too soon. Give your property a fighting chance with a good time period and a VERY competitive commission. A property has to be sold THREE times: First to cooperating agents (they have to sell it to their buyers), second to a buyer, and third (which most forget) the BANK! If there is financing involved, NOW MORE THAN EVER, banks need to be convinced of its value too. P.T. Barnum is credited with saying "There's a sucker born ever minute." Thought a buyer might think a property is worth $X, the bank may say it is only worth $X-20%. It is a LOAN TO VALUE, not loan to purchase price!
Terminating an Exclusive Right to Sell: Although it is a contract with a predefined start and end date, if you are that unhappy with your agent/agency, let them know and give them the opportunity to remedy the situation. If they're unable or unwilling, a lawyer can guide you to get a release.
FSBO while listed with a Realtor: Why compete against yourself? You're paying, regardless, your Realtor so let them work; that's what we're paid for!