For years I've used a multi-effects pedal for pretty much everything I do, but recently I thought I'd give assembling a pedal board a try. I've got the tone and pretty much everything how I like it but I'm having a couple of issues and could use some advice since I'm pretty new to this whole thing.

Initially I had everything in series, tuner > distortion > eq > wah > delay > amp, but I got an incredible amount of buzz coming through, especially when using the amp distortion (even when the distortion pedal was not active). If I wanted to continue using this set up, is there any way to minimize the buzz?

I tried switching it all to the effects loop which eliminated the buzz entirely and sounded pretty great, but when using the distortion pedal it cut the volume massively for some reason, any ideas why? Additionally, and this is the thing I'd like advice on most, the wah started sounding weird, basically it cleaned up the amp distortion while it was on, dropping the gain quite a bit, and when at the bottom of the wah range the volume drops massively so you can barely hear it. The wah is pretty old (I bought it when I was a kid then ditched it for the multi-effects) so it could just be it's ****ed, but it seemed fine when running in series.

If anyone has any advice I'd be very grateful. I'm running this all through a Marshall JCM 2000 dsl 50.

Try running the wah 1st, then the tuner. I run mine this way & seems to work fine, I use a standard Cry Baby & a Boss TU2.
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Jimmy Fuzz, when you placed the distortion and the wah in the effects loop they did not operate correctly, but there is nothing wrong with your pedals. Simply wah and distortions should never be placed in the effects loop (generally speaking).

My favorite setup is:
Tuner > wah > Distortion > amp in> effects loop send > EQ > Delay > effects loop return.

also you may like eq before distortion or wah after distortion. Either way do not place wah or eq in effects loop.

you may want to experiment as anguskilminster said with wah and tuner to get a better use of wah. A lot of people have a problem with a particular pedal at the beginning of their loop and thus place it before the tuner.

note that distortions, eqs, wahs and compressors generally add noise to the signal. and to be able to understand your signal path it would be better to know the model of each pedal to asses the pedals in terms of noise.

finally i must add that unless you are running the pedals on batteries, the power supply may be part of the noise issue.