6 months on L type visa?

Hi. I'm from the UK. My girlfriend's work are sending her to Beijing for 6 months from June and I want to take a sabbatical from work and go with her. She will get a Z type provided by her work and I have to sort out my own. Ideally and if possible, we'd like to see as much of PRC as we can but also visit other countries. I've read that the tourist L (for me) can be either single or double entry, each lasting 30 days. As we want to travel round, would it be best to apply for a double entry L, fly out after 30 days to say Japan, fly back into PRC and then fly to say HK after another 30 days to renew it and if possible apply for a 6 month multiple entry type? Or am I dreaming? Are there any rules/problems with renewing or extending? Thanks for any help. Phil