So I'm 6 months in, and here's my experience:
I ended up signing up with Wings Over Asia who are kindof a regional FBO stroke club stroke dealership stroke... Whatever they are they have been incredibly helpful and the flying community here seems alive. There are a large number of members, not sure how active they are. I've been flying DA40/SR22 and I've clocked up about 50 hours since i've been out here. The rental rates are comparative to equivalent aircraft in the UK, and I've not run into availability issues. WOA members have been absolutely great, and the scale of the flying is above and beyond what I expected. Since arriving out here i've flown (VFR) to Langkawi, Pengang, Melaka, Tioman, KL (Subang) in Malaysia, Hua Hin, Hat Yai, Bangkok, Chiang Mai and Phitsanulok in Thailand and I'm planning trips to more of Peninsular Malaysia and across to Borneo in the next 6 - 9 months. It's true that the weather can be hazy, and the afternoon thunderstorms are to be avoided. Also many controllers further north in Malaysia and into Thailand don't seem to fully understand what VFR means, so I'm currently working towards my IR to try and simplify that. Landing fees in Malaysia are a bargain ( Landing + 3 nights parking in Langkawi was < 4 GBP). Thailand can get expensive with Handling charges. Also getting used to the Coms can be a challenge - in particular place names combined with a local accent can be tough but after a few flights you get used to it. VFR routes can be very low and sometimes seem to lead you straight into hillsides, but provide useful ways to get through the controlled zones. Customs/Immigration wise there is a lot more paperwork than I have found flying in Europe, but its pretty simple once you have the hang of it, and I have a spreadsheet which produces all of mine for me before I fly. I've flown to some great places - landing at Tioman with its 'no go arounds below 200ft' rule gives a real sense of adventure, and the approach to Langkawi international over the Archipelago is breaktaking. The dramatic aspect of Penang from 1000 feet is also something that makes you glad you have a pilots licence.
Thanks again to everyone who gave me tips, and thanks to all the people I've met through WOA who are making the flying amazing fun!