Wow, James, you're my hero now! Most guitarists think the bassist is just some dumb guy who can't handle playing more than one note at a time, or more than four (or five) strings

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As far as recording bass is concerned, there are many schools of thought on that, but depending on who your intended audience is (and your clients, if anyone butt yourself), it comes down to experimenting and deciding what you like best.
I used to religiously follow the advice of the "pros", until I noticed that I liked the sound better on vintage recordings than in newer stuff that represented the advice of the pros I was listening to

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So a few years ago, I went to a dual approach of combining the miked cabinet with the direct signal. For the direct signal I use my Avalon U5 DI (it's sort of a preamp, but the boundary between a DI and preamp can be hazy).
I initially thought I would mostly use the miked cabinet in the mix, but find that I use more of a 2-to-1 or even 3-to-1 ratio favouring the direct signal. I find that the miked signal helps add some warmth and personality to the sound (which is to be expected, as it is the sound that I react to when I am actually playing), but the direct signal is much cleaner and purer and easier to work with in the mix.
I apply very mild compression to the direct signal, but none to the miked signal as a cabinet already compresses the signal somewhat. And really I am applying peak limiting more than actually compressing the signal, just to avoid notes sticking out in the mix and becoming a distraction.
There generally is a delay in the signal reaching the mic vs. the direct sound, so in most cases I find I need to invert phase (not a technically accurate description of what that plug-in does) . This I do by ear, as it is an inexact effect since the signal may be off by less than half a period and so shifting it may do more harm than good. Yours ears will know.
I currently use a single Aguilar GS112 12" cabinet, and I stack it above a rack and use a floor mic stand to point the mic at an angle towards the middle (mid-way from the centre to the edge) of the low driver. I eyeball the distance but my guess is I position it about 4" to 6" away. My preferred mic at this point came from a gazillion on-line recommendations, and is a general purpose mic also favoured by drummers: Sennheiser MD421 mk II. I don't bother shock-mounting it when using it with the bass cabinet.
I generally play the bass at moderate volumes when recording. I need it to be loud enough that I can hear my own dynamics and thus play cleanly and consistently, but no louder. Judging by the settings I use on my power amp, I would guess that I play at half my normal volume when recording, which is about equivalent to the level of someone talking quietly.
For my particular setup of instruments, etc., I have found that this gives me the cleanest and most consistent signal to work with, and requires a minimal amount of post-production compared to other stuff like drums and guitar. But this is just one person's experience.
As for guitar, I don't know, because I no longer own a guitar amp and am not a good enough guitarist to want to record myself anymore. I cheat and use sample libraries at the moment, because they sound better than my own playing. One of these days I hope to find time to resurrect my guitar skills (I was a fairly proficient jazz and folk guitarist before I ever learned how to play bass, but that is by now many years ago).
In terms of basic tone quality though, I did a recent experiment and found that using my recently purchased Summit Audio TA100 half-rack tube amp (or DI if you prefer that terminology), seemed to come the closest to giving me a basic electric guitar tone that I could work with -- as opposed to something so clean and uncoloured that it sounds semi-acoustic.
The Avalon U5 also helps add some initial character to electric guitar, and a few years back I had great success using the ART MPA tube mic preamp series.
I haven't yet tried the guitar emulation mode on my RME Fireface, but plan to do so fairly soon. And I intend to record the guitar fairly clean and use Guitar Rig after-the-fact for effects (though using it in monitor-only mode during recording). I also find Guitar Rig to be useful in making a guitar sample library sound more like the real thing.
Hopefully someone else can chime in with direct advice about miking a guitar cabinet. Some like ribbon mics, some prefer two micsc at different positions, and the standard is the Shure SM57 pointed at an angle towards the cone. I have a Sennheiser Evolution 906 guitar amp mic that I bought recenty but haven't yet had a chance to try. Anyone local to the SF Bay Area who'd like to try it out, get in touch with me as I would enjoy having a reason to use it (my own playing wouldn't show it off properly

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