If there are enough channels available use both a di and a mic. Remove any pedals from your signal path don't need for a particular track to avoid any adverse impact on your tone (even your tuner). Don't worry about string noise on the di. It won't be as obvious in a mix, it can actually help the bass part stand out and hey, bass is a stringed instrument! I'm sure the recording engineer will check but it's essential to make sure the di and mic are in phase. If the di is after your pedals it will pick up your effects. Talk to the engineer about using your compressor. He/she may well have a vastly superior unit compared to your digitech so you might not want to use yours. If you do, use less rather than more compression. It's difficult to compensate for overcompression and it's important to remember compression multiplies not adds, eg if you compress at 4:1 and so does the engineer at mixdown the bass is going to be compressed 16:1, pretty savage. You could try using the digitech after the di so the di is uncompressed but the mic is compressed, again talk to the engineer. New strings, set up your intonation properly, new batteries in anything that takes them. Don't get too serious at the session. Do a good job but remember you'll deliver a better performance if you're enjoying yourself. Trust the people you're working with (you probably don't have a choice) and learn everything you can. Also 'getting it right the first time' sort of implies that you will never learn anything and get better, when of course you will. If this is your first recording experience don't be too hard on yourself (or the band) or expect perfection, it takes years to get years of experience. And of course, make sure the band is well rehearsed, has a plan for the day (is the 8 hours all tracking time or does that include mixing? when are you going to do the vocals?) and get the drummer to show up *early*. Have fun!