That seems a bizarre combination of gear. The MD8 was a great multi-track recorder ... in 1998. But not now.
Still, you are where you are, and what's missing from your line-up is effects processing. The MD8 doesn't contain any built-in effects processors for adding things like reverb and compression to vocals and non-electronic instruments, such as guitars and drums. You really will need that to make your recordings sound anywhere near professional.
Most post-MD8 multi-track recorders had built-in effects, which makes things easier, especially for the newbie. But you'll have to get separate units to work with the MD8 and a whole bunch of cables too.
At minimum you need a reverb (or multi-effects) processor and a compressor to add to your line-up. Companies like Behringer and Alesis produce units of this type at the cheaper end of the market so would be worth checking out.
