re: Mixing Effexor(SNRI) with Paxil(SSRI)?
I suppose it would be fine to do, but I don't really see the need to do so. The SNRI would work on serotonin and norepinephrine whereas the SSRI would work mainly on serotonin.
I'm assuming you're self-medicating, though, since you obviously wouldn't be asking a forum this question, but instead, your doctor. When it comes to meds like Effexor and Paxil (the 2 most notorious withdrawal-symptom-inciting meds), I would not take them without the help of a doctor.
Also, if you had side-effects from the Paxil in the past, what makes you think you won't get them this time around? Do you think the Effexor is going to help you with the side-effects? Because it won't. I would simply get rid of the Paxil, since you have already tried it and didn't like it, and simply stick to the Effexor, and you could use the money saved from not buying Paxil and put it towards the Effexor (or you could put it towards a visit to the doc, which would seem the wisest choice).