In reply to rare-name:
A tricky question to answer. What one person finds physically and / or mentally demanding another may find easy. Fitness, stamina, experience, skill levels, familiarity with the terrain, nutrition and route conditions are some of the variables.
Personally, I would find this fairly straightforward in reasonable conditions but be aware that tackling what some people would find tricky ground such as Crib Goch after doing Tryfan means you may be extra tired and possibly more likely to make mistakes. There are other people who may find doing Tryfan quite enough, others will happily do all the three thousanders in a day.
The best preparation, if you are unsure, would be to do several increasingly long days walking and scrambling until you feel confident in your ability