Getting hold of Bella is complicated, you're best off just downloading her, you can find her on many sites, including the sims2 official site, just search for Bella in the users area and you'll find many.
To get a working car you'll need the nighlight expansion pack, to get a car as a lawn ornament, you can download a mod at modthesims2.com, (the premier site on the 'net for sims mods) by carrignon I think, but check to make sure.
To get rid of the blur, you can do this two ways, the easy way, and one that will cause problems with patches, etc. is to patch you game executable with a hack from gamecopyworld.com make sure you make a backup of sims2.exe first.
The "safe" EA sanctioned way, is to add the following:
intprop censorgridsize 0
To the file "userStartup.cheat" in the
My Documents\EA Games\The Sims2\Config
folder, (My Documents is usually located on the desktop)
If the file userStartup.cheat does not exist in the folder above, shut down your game, create the file, add the intprop command and restart your game. It will get rid of the blur, and leave you with barbie doll Sims. (no private parts) If you want nude clothing, or default nude skins, then you can get them from modthesims2.com in the downloads area. You'll need to register and login to get access to the adult area. You can also find working genitals (male and female) there too, as well a gay body builder mesh, should that be what floats your boat. You can also find a muslim headscarf, etc. As well as Motobikes, and celebrity sims, etc. They have all the best content. thesimsresource.com has banned people from talking about them in thier forums for this reason.
To make your Sims younger you need The Insiminator mod from www.insimenator.net you can also get the inteenimater (which does the same thing for teens too) This allows things like teen wooho, etc. It's a multiple hack mod, that allows all sorts of things.
Failing that you could just turn the aging off, which you can do from the cheat menu. (control-shift-s) then type:
aging off
and then:
exit
To quit out of the cheat mode, you can also type:
help
Within the cheat mode to find out more about what it can and cant do, though some functions will need to be turned on manually before you can use them, you can use the:
intprop censorgridsize 0
Cheat here too, if you're too scared to alter any system files.
There are also some good mods to be had at www.valdea.com which has the worker & wohoo NPC's which mean you can have a live-in NPC maid, and also earn cash from a bordello, running male and female prostitutes if you wish. You may also want to seek out Liz Love's "lovebed" which allows your sims to wohoo with people they don't even know. All of them are safe and play tested. But check the forums at modthesims2.com if you want to be sure.
However if you're underage and you don't want your folks seeing any of this, just leave it all alone.
up to you really.