Honda Accord 94 due for servicing bad

Can I email someone here with a few questions and some help on my Honda Accord EXi 1994 CD5 possibly? I live in Perth and have been holding off for a while but should get something done at least.

It has a few problems and is due for a service. I have posted here before but have forgotten how to find my old posts.

Few issues are listed below, pretty much I would like to do service etc myself and save money:

1) Auto trans fluid requires change/flush - is this complicated and should be done at mech or can a noob undo the drain plug and flush it out and pour in more. quoted ~$150 with Honda OEM for trans fluid

2) I've read the sticky on the paper clip technique on readin gerror codes. My dash lights still come up and I fear the daage is done or is continuing. Had various mechs tell me various things about the lights ad error codes.

3) Tried to do a service but couldn't find the oil filter so all Iended up doing is draining the motor oil and replacing new oil. Also what was the recommended motor oil type again? 20/50 or something.

That's about it for now thanks.