If you start in Jan, you'll finish the following June. A load of us got interviews and jobs within weeks of finishing, so was just the right time for us. Don't worry too much about this though, different airlines hire at different times. Flybe and Ryanair are all year round, easyJet seems to be May-September, but also Monarch, Thomas Cook and a few others have recruited unexpectedly too.
Groundschool, definitely do it in the UK. NZ was enjoyable, but Clearways is very isolated. 8 months was definitely a LONG time, let alone adding ground school onto that...quite a few cadet blogs going around that might be worth reading.