I'd like to add another outlet in my basement, and since it will be near a utility sink, I think a GFCI would be appropriate. There are outlets nearby, but they all appear to be in the middle of existing runs. I'm sure this is a very basic question...but can I tap into one of these to run the GFCI, and maintain the run to the other outlets in the line?

I understand that I'll have to account for the load that I'm putting on the circuit (I think that's the right terminology).

I have a similar question with regard to installing a bathroom fan in the basement (sectioning off part for a darkroom, and want to vent out the air). Can I "interrupt" an outlet run to wire the fan (which is only .45 amps), together with a switch for the fan?

Finally, is it okay to do this work on my own, or do I need to get an electrician in order to meet code and keep my insurance viable? There seems to be lots of advice on the web about doing this yourself, but I figure I should ask.

Thanks.