Congrats,that should be a great machine to begin learning multitrack recording on.I have the Tascam 464.Not sure how it compares,but I think Tascam makes the best cassette multitrackers.
Why is there 8 inputs, yet its a 4-track.
This is so you can mix multiple instruments at one time.You can use the mixer to send a combination of instruments to a single track or combination of tracks.I have the Tascam 464 which can record 4 tracks at once.Not sure if your machine can do 4 or just 2 at a time.But you should read the manual,and experiment with the mixer to get a feel for how things work.
Why does the manual tell me to record with the PAN all the way to one side
When recording your tracks,you use the pan knobs and the track select buttons to determine which track the recording goes to.Usually if you pan the channel to the left,then that channel will get recorded to any odd numbered tracks that are selected and if you pan it to the right it will go to the even numbered tracks that are selected.When mixing your tracks down to a stereo two track recorder,the pan knobs determine where the sounds sits in the stereo field...eg. left or right.
What's with the SUB-INPUTS? And: What should I use to send the final peice to my computer - the TAPE-OUTS or the LINE-OUTS.
Not sure what the Sub-Inputs are...you'll have to refer to the manual on that one.You should be able to use the line outs to send to the computer.Unless you have a pro soundcard,you'll have to get a special cable that will go from two 1/4 inch mono(or rca,not sure which your machine has)down to one 1/8 inch stereo.Then you can plug it into a regular type soundcards line in.
I don't know anything about midi stuff.
Hope this helps you out.Like I said,I don't have the same model Tascam as yours,so it might be a little different,but I bet it is pretty similar to mine.My manual kinda gives you a walkthrough to get started recording a couple tracks.I don't know if yours has that or not,but you really should read your manual through and get familiar with all the things your machine can do and then do some experimentation to get the feel of it.If the manual suggests a certain type of tape,try to use that kind for best results.It made a world of difference in the noise levels on mine when I used the suggested tape.