eight tracks...
yes, 30 seconds or so between the tracks is perfect...
here's a couple more ideas that might help you get a good sound... i say good, because in well over a decade of cassette multi-tracking, i have never heard anything that has a great sound from myself or any of my many talented peers... of course there are great performances, emotive and amazing, but the fidelity is what it is and that element forces you to make material that transcends the limitations... it's much easier to be mediocre and get away with it if you have a budget... imho, we have a hundred years of recording to back up that theory...
mess around with all sorts of stuff by yourself... try out different microphones... different instruments... use the whole room... try to isolate and eliminate the hums and grumbles from the electrical system... you are gonna get some hum, but you can make it so you have no line noise or at least not much without really expensive power conditioners... turn off nearby televisions and computers and turn dimmer lights either all the way on or all the way off...
once you are familiar with the machine, try to get all the basic tracks of music recorded live... it puts just the right kind of pressure on a band to know that it is a moment to be captured... make sure you play the very loudest song for a soundcheck and levels and allow for the inevitable fact that the band will be even louder when it is showtime... once you have things dialed in, make sure that the guitarists and bass player leave their volume alone... i know it can bruise an ego, but be honest if you already have enough coming in and it sounds good... from a technical standpoint, this will make all the bleed between mikes make sense and with 8 tracks you have plenty of room for separating everyone and vocal overdubs later... because you are cramming so much stuff on a little strip of tape, it is very important to record the bass and drums on the outside tracks -- 1 and 8 -- so if they are a bit too hot (loud) they can only spill into one adjacent track and not two...
try to isolate the drums as much as possible... blankets, an old couch or futon mattress behind a kit and it can take alot of the sound reflection out of the wall behind the drummer... stuff a sweater in the kick if it is too loud... punk is nice because for the most part the drumming is old school and not alot of dumb extra hardware clutters things up, but if you have a guy with four toms who can't tune them, it might be time to have him try just a snare, kick, ride and high-hat... high squealy guitars? kill the high hat and tune the snare down... swirly thick fudgy low fuzzy guitars? let the snare snap a little more and be less afraid of the high-hat... it is best to keep the snare and overhead mics away from the high hat to avoid hearing nothing but hiss... drums are a nice flavor in rock, but i think cassette just doesn't have the dynamics or the room to have the next geddy lee or whatever... get all rock-a-billy though, and it can sound amazing... there is a very short line between eddie cochran and the clash and understated, but tight and powerful drumming is the key... in my own music, i have found the styles of hal blaine and ringo starr to be more effective than keith moon... it's not a judgement call, it's just the medium...
i have also found that electric guitar is best recorded by turning up smaller amps to a sweet spot rather than trying to mic and isolate a big stack... some rediculously small amps have been used on some very loud rock from the sonics and dave davies of the kinks on down to the present... a fender champ or a slightly modified channel from an old tube tape recorder -- roberts and akai are favorites -- makes a fantastic studio guitar amp with plenty of crunch when those little tubes drive a big speaker without bleeding into all the other microphones...
give the bass player -- at the very least -- headphones and use a DI box... make the bass player buy his own and he or she won't lose yours... it is a really simple passive device that makes it sound nice going straight into the machine... if he or she wants a little more warmth, for a few more bucks he can move up to one of the so-called mic preamps they sell for around 50 bucks that really only sound good on bass... for cassette multi-track, the bass sound is the toughest, but whatever you do, don't resort to a mic on the speaker... you can go mad trying to make that work... just send him or her out for a direct box at the least... he or she will need it live anyway...
if the band needs a vocal for reference, put the singer in the middle if you can so that everyone can read his or her lips... try not to record an amplified voice, but a direct mic from a live take is alright if the tinkering is done... live vocals are fine in everyone's headphones, but having a bad lead to mix around later when the lyrics and cadence have changed and the old version is under everything is impossible to fix, so no pa unless the arrangement is set in stone and then a little won't hurt...
at this point i would avoid bouncing tracks, trying to get quality separation on a mixdown of eight tracks is enough trouble without trying to take care of phase and level issues down the road... i am guessing that you don't have $1,000 speakers... few of us do... if your machine has 8 outputs, i would find a friend with protools and a tile bathroom... if you have that, you can record the music with all the leads and whatnot, dump it into his or her box and overdub the vocals right there in the bathroom... because it is on the box, you can do endless takes without stretching your masters or worse yet, having them eaten...
to avoid having tapes eaten make sure you have:
a) clean heads and roller
b) a fully rewound tape between days of recording -- don't just pick-up where you left off tuesday, tension changes in no time at all...
c) even power -- i once worked in a place where the pitch changed when the folks who lived upstairs used a toaster oven and another where the fluctuations from a distant space heater instantly messed with the servos on my transport and made them run in opposite directions...
d) store your tapes in your dresser... most folks have a nice dark and dry dresser... most musicians have a clean clothes pile and a dirty clothes pile, so there is plenty of room for masters in the dresser...
most of all, have fun... in the end, i think the fun of a moment is what you are trying most to capture when tape spins... some accidents are still legends, so don't be afraid of the lumps... that is part of what is charming about lo-fi... i hope some of this was helpful to you... good luck!