I am planning a multi-day hike in the White Mountains,NH in the middle of May. I would like to hear your opinion on clothing and some gear you consider necessary for this area at that time of the year. I can't decide on the insulation layers. Would a DAS parka be an overkill? Would a Nano puff + a fleece vest be enough ? Should I go with regular nylon hiking pants or softshell pants are a better choice?

It will depend on the immediate weather and where you are going. Likely the Nano and vest will be fine. Nylon pants will be fine. you will be in the dead middle of bug season and likely have some mud too with all of this snow. Hell microspikes may even be a good idea if the monorails stick around.. you figure middle of may is only 8 weeks.. they just got another 12"+ in the mountains this week.