Recruitment has been heavy on the Bus lately, with the Bus taking over from the FLUF down at LGW most DEP's can expect that.
777 has gone VERY senior as a fleet, don't know if that's due to an anticipated dual 777/787 rating as the cockpits are compatible.
There is a fleet swap window running at the moment with lots of people bidding off of the SH roster onto the LH. That should cover LH manning requirements for quite some time I would think.
As to previous type qualifications I don't know where you stand with having the 777 already. You can but ask!
If you DO get DEP 777, expect to be on blind lines, i.e. work allocated to you and every weekend flying, for a very long time.