I'm not sure about the ascetics. As you said, it carries over to NG+ so subsequent playthroughs are innately harder than normal, so using them at a bad time or with an underpowered character can severely screw you over. Not only that, but it cheapens item farming and boss souls, since you can just ascetic as many times as you want to get as many items/souls as you want, thus removing the hard choice of boss soul usage and dissuading the transition to NG+ since there's little benefit to doing so. Frankly, since you're given little information about what changes with each ascetic, I wouldn't use them until you're confident both in your abilities and gear. Otherwise, you're just going to get stuck.