Whats the best time on friday for one to take haircut, cut nails and shave? Is it before chatzos, or does it matter?
Unlike erev pesach, there is no prohibition on doing melachah after chatzos on Shabbos, and on the contrary, there is perhaps a virtue of taking a haircut and cutting nails after chatzos, in that it is clearly in honor of Shabbos. However, one should only do this if it won’t place pressure on Shabbos preparations, and one will be able to enter Shabbos calmly.
Sources: See Magen Avraham 285:1, who mentions cutting fingernails after chatzos on Friday (before reading shenayim mikra); Arizal is quoted as having cut his fingernails after the time of minchah gedolah (Shaar Hakavanos 6).