I have been using 2004 cockpits as I have yet to stumble across a 2005 cockpit set. Only problem is Red Bull but I ain't fussy so I just use Jaguar anyway. See the 'Season Packages' section of the downloads page.
Tracks are available from various websites including this one, although few, if any 2005 spec tracks have been released that are compatible with GP3 1.13 (other than the Belini couple of tracks that work). Still, there are enough 1999-2004 tracks to keep you happy for many hours, and a host of non-F1 tracks too. Installation instructions are included in the readme file inside the download in all cases.
You didn't mention GPxPatch. Get it!
As for the 11th team - most carsets released since the F1 field dropped to 20 cars already contains a fictional or lower formula team. If you wan't to create your own design then go ahead. It takes a bit of work if you are new to carpainting, but it's worth the effort. There are blank car/cockpit/helmet templates available from the downloads section on this site.
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The test of a first-rate intelligence is the ability to hold two opposed ideas in the mind at the same time, and still retain the ability to function. -- F.Scott Fitzgerald