Looks like you have a Prather Lapcat II with the K&B 7.5 like you said. A nice boat!

For fuel you need glow fuel made for boats. At least 18% probably not more than 20% oil and a nitro content of 20-65%. 25-40% would be good to start. You can buy this online at many places. Or at your local hobbie shop. Buying local you don't have to pay hazmat shipping but it will usually be more if they even stock it.

Does it have a radio? If not a simple AM radio will work such as [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXASX2**&P=0]This one[/link], or you can always go nicer. If it has one, put some new batteries in it and see if it works. For servos a standard servo is fine for the throttle, but you will need two high torque of at least 100oz/in each for steering. Metal gears is recommended because of the strain on them from the engine. Also Two linked with a Y harness is also recommended over a single larger one for extra strength in the servo horn shaft. [link=http://www2.towerhobbies.com/cgi-bin/wti0001p?&I=LXDWF8&P=0]Ones like this[/link] would work well.

For running the engine you need a good glow plug for the engine. A glow plug igniter, and an electric starter like the type used for airplanes. And a battery for the starter. Note: you will have to switch the starters + and - because the outboard engine turns the opposite way from and airplane engine.

A new friend that know's boats that could go to the lake with you would also be great.