sometimes I use a compressor on the main bus (the mix bus - I think that's what I call it). If so, I turn it on early in the process and mix into it, so to speak. I try to leave a lot of headroom while I'm mixing - that may just be personal preference, but if I get stuck up close to zero, I start running into problems - painting myself into a corner, sort of.
I don't use a limiter while mixing. If I'm clipping, then I need to turn everything down to get a lot of headroom like I mentioned above. If I'm making a mp3 to send to a client to ask a question or something and I want it to be louder, sometimes I put a limiter on and slam a little, but that wouldn't be part of the final mix.
I try to send mixes for mastering with lots of headroom. The mastering people I've talked to (mastering in the digital realm), really couldn't care less, it turns out - they just turn it down if they need to. But I still go for at least -20 RMS anyway. It makes me feel contemplative and mindful.
If I'm mixing into a compressor, I really don't ever turn it off - and definitely not for the final mix - it's part of the sound at that point. If I had done the mix without a compressor on the main bus, and then added one at the last minute and liked it (this has never happened because I haven't tried it), then I'd probably send both the compressed and uncompressed mixes to the mastering person. But if I used the mix compressor from the beginning, then it's pretty much a disaster to take it off - the mix falls apart.
I usually use a hardware compressor for this purpose, which presents recall problems if I use it for something else before I'm done with the mix, but that's not a huge deal.
As far as EQ goes, I do a lot less of that at the full mix level, but if I tried it and liked the result, I'd definitely keep it. I have a hardware EQ that I sometimes use on the final mix, and usually after I've done the work. But I often wind up taking it back off, or making adjustments that are so minimal that it probably may as well be off. The mastering people have much better rooms (and ears) than I have, and so I pretty much leave those details up to them.