I'm impressed that you did as well as you did on your first part! Making parts is unfortuntaly complex, and it doesn't help that it is poorly documented at present (although we are trying to change that). The first one of these describes (with later modifications and more yet to be done!) how I made my first very simple part. Things like editing for the px ending are in there. I'm working (slowly though 
) on a python script that will read either an svg or preferably the fpz file and correct a few things that Inkscape does that Fritzing doesn't support (px on font size, style command replaced with inline xml) and checks for errors such as missing layers and missing terminal connectors in the svgs that are specified in th fpz (and changing legacy silkscreen color of white to black, although that one is a Fritzing change) but I'm not finished yet (and then I have to document it ). Here is a pointer to the latest parts tutorials such as they are (you may already have seen them though):
Yes, at least sort of, I usually start with a generic IC from the core parts bin and change it to have same (or more) number of pins I need for the new part and change the metadata with parts editor (because its a little easier than with a text editor) then export the part. Now I have the correctly formatted and laid out files to edit to do what I want. I may still need to add or remove pins but at least the basic layout is there. As well the part is correctly registered with the parts data base which needs to happen even if I was to start from a new file.
This one unfortunatly is an Inkscape feature. Even if you start out with minimal groups as you edit it with Inkscape it adds extra groups and transform/translate commands (which I dislike). The only cure I know of is after finishing the editing in Inkscape is ungroup all the groups and remake only the groups that need to be there (although you then need to know what groups need to be there and there order again, but that comes with experience). That removes both the groups and the transform translate commands but is extra work (and the svg will work without doing it).
Peter