No limit, you can have as many as you can be arsed dealing with. Usual fee is 3% buyer and 3% seller but its open to negotiation - lot of seller and buyers don't want to pay it so they try to get the other party to pick it up. Only the successful agent gets the bunce.
If its a "saleable" property, then worth trying to do a deal with an agent for sole agency status in return for a reduction on fees. Some do, most don't.
JF