First thing to do is marking only stalls on research and putting the research on maximum, since you don't have any food stalls to begin with the scenario. It might take a while, but after a few stalls, you will get a Hot Dog Stall and, after that, a Fries Stall. After having those, mark thrill rides and roller coasters, since you will need a lot of coasters to attract the required guests.
The three pre-built roller coasters can be handled two different ways. You can either let them be, as they are a great guest magnet and money makers, or you can destroy them for a pretty nice cash bonus and build one or two small roller coasters by yourself. If you destroy them and repay your loan immediately, you have a whopping $36,000 to work with. Either way, there are a lot of gentle rides available from the start, so you should build a few right away.
Just keep on deveoping your park around the pathways (which don't have nothing wrong about). If you lack some space later on, you can expand at the back area or, before that, even at the right of the entrance (there is a nice hilly forest which is around the section where the coasters agglomerate). Just place a few Information Kiosks so that your guests can buy maps, as your park is pretty big and they might get lost if you expand your way-net.
Notice that your guests aren't that poor but, even though, if you set your park as a pay-per-ride, most of them will likely be out of cash and leave too early (as you have three grand coasters at the beginning which can generate a good profit but, on the other hand, wipe out your guests' pockets). If that happens and your guest count stagnate, reduce your prices a little when you reach the point where money is not really the biggest of your problems. This should make sure your older guests stay in your park for a little longer while more come and, thus, your guest count slowly increases again.
The scenario objective at first may look hard but as you'll see, with the great three coasters you start with and with many more good rides you'll research, this park is not hard at all and shouldn't make you face much problem.