Hi and welcome to the forum.
If it aint broke, dont fix it. These engines are very good and not known for building up loads of c--p. You could consider an oil flush rather than dismantling the sump. Before you take any action have a look at this http://www.carbibles.com/engineoil_bible.html which contains comprehensive advice. Note there is a warning towards the end of the article. I would sooner buy some cheap oil, but of the correct viscosity, and fill with this without changing the filter. Run this for a few miles, preferably getting the engine well warm, before doing an oil and filter change in the usual way. Being a Yorkshire man, I would save the hardly used oil for the oil can.
Regarding the other work you propose, apart from visual inspection of everything in the vicinity, you could also look at distributor caps and rotor arms and HT leads.