[sdiy] starter components -- one of everything?

[Johannes Öberg]

I found a cheap surplus supplier, and now I'm wondering what OP-amps
and OTA's are best to get for general purpose use. I see some op-amps
feature "offset nulling". What is that?

What I'm mostly considering building are a couple of compressors,
filters, distortions and stuff like that, and various control stuff to
make stuff MIDI-controlled. Are those packs of 4-opamps-in-a-DIL14 a
good idea too keep things at equal temperatures or something?

What's the difference between the different OTA:s? Can you safely
replace one type with another in circuits, even if you don't really
know what your doing? :-)

Also, what transistors? Are arrays generally a good idea?

(FYI, I don't know much about electronics so I'm mostly in the
'build-other-peoples-circuits'-stage of my sdiy career, I'm on a
poor-student budget and I'm not exactly and audiophile. I guess I'm
looking for best bang/buck)

> 2N3904 and 2N3906 transistors, > TL072 op amps

Are these the cheapest, the best or both? :-) That is, why 2n3904 etc?
(if there is a why)