Hi Bee. We did your move several years ago and I think there is some good advice here. I don't know how long you have been away but I would caution against over-idealising the English country village/commuting lifestyle! I think you are going to find your budget a bit of a stretch if you are looking for a 1 hour train commute - and be realistic about how long it will take to get to the station and to your place of work at either end. Also, which part of London are you heading to, as crossing London by tube can add at least 30 mins to your journey.
If you are used to Australian houses then anything comparable here will feel small. If you find a "large" house within your budget, or something that compares with what you're used to, then there is something seriously wrong with it (I speak from bitter experience...). Also bear in mind that fuel costs (heating and transport) will be much more than you are used to.
School places are competitive. Lots of people move out of London to access "better" state schools and then find they are just as hard to get into - harder in some areas as the village school, if it still exists, will be limited to 20 or so places. Secondary education becomes a major issue if you are not in the local town. In Kent I believe you have the grammar school system and all that it entails (can be good or bad depending on your perspective).
The economy here is improving but nothing like what you have had over there for the past few years. Jobs are still hard to come by with big redundancies still being announced. DP and I were both made redundant shortly after getting here and neither of us has managed to get back on track - recruiters view Australian CVs with suspicion as they are not always familiar with the companies you may have worked for, and chasing references over a 10 hour time difference is too hard when there are dozens of other applicants.
Sorry to sound negative but I wanted to share our experience. As others have said, renting may be your best option in the short term. I would add Dorking and surrounding villages to the mix of suggestions (although the commute is a pain), also don't disregard the Chiltern villages as this is one of the best commuting lines into London.