Make your enlarged negative. Then take another sheet of film, fix it out, wash and dry. Then, place the negative emulsion side down on a light box, and tape the clear sheet of film over it. Now, do your retouching on the clear sheet - if you find you don't like the results, you can throw away the clear sheet and still have the enlarged negative to try again. Also, because your retouching will be separated from the actual negative by two thicknesses of film, the retouching will be slightly out of focus when projected onto the enlarging paper.
For retouching, you can use pencils, Spotone (if you have any), Marshall's Spotting Dyes, Veronica Cass dyes, etc - whatever floats your boat.
One suggestion - try using Dr. Martin's transparent watercolors. You can use these dyes just like Spotone (ie, let a bit dry on a plastic palate, and then use a slightly damp brush to pick up dye to apply to the negative. Using a magenta color causes your spotting to have a higher contrast if you print on variable contrast paper - that's actually ideal because it gives you better control over your spotting when you are working on details. Using a yellow dye results in lower contrast - that may be helpful if you need to apply a wash to a large area.