I'm considering getting a Tascam DP-004 for Christmas. Is there anyone who owns any of these that can tell me how they like/hate them?

I plan on doing a lot of 80's metal demos, covers, etc. with my guitar/keyboard and possibly an electronic drum set.

Also, when you guys usually record. Which instrument would you record first? What if I want vocals, guitar, drums, bass AND keyboard? That's 5 instruments and only 4 tracks. Would I switch the tracks then? When there's a part of the song with no vocals can I use the keyboard on that track then? Using these 4 tracks sounds quite confusing.
That unit sells for around $200 and for that price you could go with an interface for a computer...which would be a lot better.

It has the two inputs for drums but I don't think it will DI bass and guitar...

The interfaces for computers will allow you to record all your instruments. For drums I would get a USB to MIDI cable which is cheap.

I suggest the PreSonus Inspire 1394 or if you have something other than Vista, the Mackie Onyx Satellite. Both are great units and you should be able to track all of your instruments one at a time.

A Shure SM57 to mic a guitar amp or do vocals would be nice. If you don't mic your amp you will need to buy amp modeling software like Amplitube which doesn't sound like the real thing most of the time and will up the cost overall.

4 tracks are for very small projects or small ideas. You will run out of tracks before getting all of your instruments recorded. Recording drums takes two tracks, guitar takes one, bass takes one, keys will take two as they are also stereo.
With an interface and computer you are not limited to any amount of tracks.