There are a couple of additional factors you need to figure in which are how long a commute is your DH prepared to do and what kind of schooling you will be looking for (I get with a 2 year old this is hard to contemplate at this point but it’s important longer term!). Various places in Kent have been suggested. It’s a grammar county, only 25% of kids get into the grammars so worse case scenario if you don’t have the money or inclination for private then you could be stuck in an area with poorly performing Secondaries. For anyone contemplating Kent, this really should be a factor! We do have some good Secondary schools but they are fewer and far between than non Grammar counties.
We moved from South London (East Sheen) to East Sussex and then six years ago to outer Sevenoaks. In Kent, in my area for £550K you could get a decent sized 3 bed in Tonbridge (good private & grammar options, decent Girls State Secondary, frequent London trains, access to countryside), parts of Tunbridge Wells (good shops, restaurants, grammars, excellent Faith Secondary & an up & coming State, just under an hour to London) & in some of the villages attached to Sevenoaks (Borough Green has its own station, 48 minutes to Victoria, good Primaries, decent Secondary (Wrotham), in catchment for the Tonbridge/Sevenoaks/Maidstone grammars and easy countryside access. Adjoining Wrotham and Ightham and Platt are pretty and £550K would get you a very decent 3 bed). West Malling (on the Victoria line) town centre is gorgeous - if you don’t mind a new build you will find lots of options in Kings Hill on the outskirts for £550K. The State Secondary is awful but it’s not the only option.
Further South, Canterbury is lovely and very historic with great train links. I’m personally less keen on Folkestone but I don’t think I’ve seen it at its best either with apologies to Folkestonians!
If your DH is happy to sit on a train for over an hour then East Sussex has some great options and it’s non grammar which means you could avoid the whole stressful 11+ process. I’m not sure what the commute time or house prices are in Lewes but I would take a look. Battle (very pretty historic town) and Robertsbridge (medieval village) both are on the Charing Cross line. The train time is about 1hr20 - fine if your DH doesn’t have to go in every day or is happy to work on the train For £550K you’ll get somewhere very nice. The countryside is gorgeous and hasn’t seen a lot of development unlike West Sussex and Surrey.
We took a look at Reigate 6 years ago - I liked it but was put off by the catchment of the good State Secondary being in an area of town that we found less desirable (I appreciate this might have changed since). I’ve only ever seen Redhill from the train station and got the impression it was pretty urban and built up (but could be oh so wrong!).
Just on Rochester - I personally would fall somewhere between the 2 PPs. The town centre with its castle & historic high street is lovely. I’d happily live in one of the houses near the cathedral. The outskirts of Rochester though do look pretty identical to Chatham and it’s got a very mixed demographic. No idea what the State Secondaries are like and if you are considering it, do look at that.