Velarization, uvularization, pharyngealization

I've noticed that descriptions of the "emphatic" consonants in Arabic
usually say that they are pharyngealized, but sometimes they are
described as velarized instead. Also, the tilde diacritic through a
letter (not above it) in IPA is described as "velarized or
pharyngealized". For this reason I am led to ask: do languages which
have velarization or pharyngealization generally not distinguish
between the two? Are speakers free in any given utterance to select
velarization or pharyngealization or something in between?

Also, there doesn't seem to be much mention of uvularization out
there. Is this because of the continuum between pharyngealization and
velarization that I hypothesized in the above paragraph? Does any
language have uvularization separate from either velarization or
pharyngealization?

Finally, when pharyngealized consonants are pronounced in (e.g.)
Arabic, the pharyngeal component doesn't have a fricative character,
does it? Is it similar (or identical) to pronouncing a consonant and
a pharyngeal approximant simultaneously?

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