Hong Lok Yuen is a about as close as you get to a proper suburban estate in HK, what I mean is apart from some apartments around the centre (it's a small centre but has a big Park N Shop and a clubhouse) it is mainly houses of different shapes and sizes - so very appealing to those not wanting apartment life.
The big houses are expensive though and usually sell for anything between 10 and 25 million HK. But you will get tonnes of room, a garden and a pool. Don't know about rentals, best bet is to go there and speak to the agents placed in the centre. They all speak English, as do most of the people who live in HLY - the place is extremely affluent and as such attracts wealthy people from all over.
The nearest KCR station is Tai Wo, and you will either catch a minibus, taxi or double decker to get there. Minibus or taxi is more convenient as the large buses do not enter the estate but stop at the main road sitauted by the entrance to HLY. If you walk it it is about 1.5 miles from the main entrance road to the estate. You can walk but it isn't the safest routes as the buses tank it down the road at astonishing speed.
From Tai Wo KCR you are looking at about a 15 to 20 minute train journey to Sha Tin.
HLY is full of westerners, so no problem meeting anyone, plus the clubhouse acts as a local meeting place as well as providing recreation facilities. I can't imagine there would be any isse with you meeting new friends.
It is also situated at the entrance to Lam Tsuen country park which has some of the best spots for sightseeing in the NT if you love big mountains and some nice hiking. However, it is not the most convenient place for your reuquirements.
Tai Po is my favourite place ( not just cause I live here). However, in terms of accomodation you won't find the large houses that are available in HLY unless you move into the Wun Yiu valley and get a place such as in JC Castle (built by Jackie Chan), which may appeal - but again top dollar, very much like HLY. You will get a large apartment in a managed block (such as the Paragon or Grand Palisades) for your budget - easily, these places have clubhouses also with gym, pools, etc. Both of these places are a sweaty 10 minute uphill walk from Tai Po Market KCR. But obviously these kind of places have shuttles that run to and from the station for the cost of about 2 dollars. Tai Po KCR is about 10 to 15 mins from Sha Tin.
For somewhere a bit more interesting (and closer to Sha Tin) you may want to try the area around Tai Po old road - it has some really nice apartment blocks such as Deerhill Bay (built by Li Ka Shing) and others. It is also a very short minibus drive away from Sha Tin town centre which takes about 15 mins from there. However I can't comment on the social life although the CUHK is also just around the corner as well the the Japanese International school (want your kids to learn japanese?).
If you need recommendations for a good english speaking agent in Tai Po then feel free to PM me.
Sai Kung is nice but not so convenient. Majority of housing there is village houses but there are some nice developments. One of the appeals is of course being on the coast and it is very popular with westerners. I go diving around there myself and you are right next to some of the best coastline in the territory. Only problem with Sai Kung is that it is about a 45 minute bus journey to Sha Tin (bus 299). However, if you are an outdoorsy type and love BBQ and a nice sea breeze then it may be for you. I would say that Sai Kung town centre isn't the most attractive of places but it is very functional and has a vast array of eateries esp seafood of course, and the surrounding countryside makes up for everything else.
Who said the NT has no soul? I guess it depends where you go as the place is huge. However, above mentioned places - very nice.