Hola Karin,
Hope I'm not too late in aswering your questions. Nevertheless, I'll give it a shot.
Q:"1 guest house suggestion that has cheap double room but isnt absolutely sketchy"
A:"Try some of the hotels in the Altamira Area, such as the Hotel La Floresta or Hotel Altamira Sur. Altamira is considered to be the safest area in Caracas and these hotels are not badly priced. If you want something cheaper try looking into the Backpackers Hostel, even though the surrounding area is not that nice."
Q:" 2 the national park thats right outside caracas: worth visiting?"
A: Which one? The Avila National Park in Caracas is definitely worth visiting. The easiest optiopn is by taking the Telefercio up to the Humboldt Hotel. The toughest trek is up to the highest peak. It is an 8 hour steep hike right up to the top, but it is certainly worth it as you can get a great view up at top of both Caracas and the Caribbean Sea, weather permitting.
Q:"3 the best way to get from airport to elsewhere if we decide not to stay; is it necessary to take the airport bus into the city and change for a bus to one of the long distance bus stations there? or is there any public transport to get directly from the airport to a big bus station...."
A:"Unfortunately the only way to get a bus to another destination other than Caracas is to go into Caracas and get a bus to your desired destination from one of the bus stations in the city. Try using private bus terminals such as Rodovias, Peli Express, Aero Expresos Ejecutivos, Expresoso Occidente (even though the surroundings are dreadful) as opposed to Public bus stations such as La Bandera and Terminal de Oriente. Private bus stations are safer than public ones. Alternatively you could fly from the domestic airport to other destinations such as Merida, Puerto Ordaz, Margarita, Los Roques among others.
Q:"4 best way to get money upon arrival"
A:"As mentioned above, the guys who carry bags will exchange some money for you. You'll get a pretty rotten rate but better than the official rate. Exchange only enough to get by and then exchange again with someone you fell to be more trustworthy.
Hope you find this info useful.
Travel safe!
All the best,
Thomas
Caracas
berry_venezuela@hotmail.com