I've done Ostend a couple of times from Biggin Hill and there's really nothing to it. You can fly direct from KOK to DVR VORs, crossing the FIR boundary at KONAN. It is a long leg over water, but the navigation is easy and you are parallel to the coastline on the European side, not very far out. Also, with that route, you don't enter French airspace, so it saves one radio change.
I fly from Biggn Hill, I have a PA28 based there. It is a fine airport with a good runway and navigation facilities if you need them, but it is expensive and a little bit impersonal for visitors. The landing fee in a single is around £32 and there will be overnight parking charges. It is open from 0700-2100 local/GMT, which means you can arrive early and depart late from Ostend for a full day.
Getting from Biggin Hill to Central London is easyish. There is a bus stop outside of the airport, with buses around every 12 minutes to Bromley South station. Buses 320 or 246. Journey time with no traffic is around 20 minutes. It can take up to 40 minutes to get back from Bromley though, if you travel between 1530-1900, as the roads are busy. London Buses do not accept cash for fares, you will need a contactless cedit/debit card to pay. There are taxis available from the terminal building, you should expect to pay around £20 each way for one as you will get ripped off for airport prices.
From Bromley South, there is a fast and frequent train service to London Victoria, with a journey time of 15 minutes. Ensure you get a fast train and not one that is stopping at all stations.
A good alternative, if you are comfortable with 500 metres of tarmac runway, is Redhill. Tucked just inside the Gatwick zone, slightly South West of Biggin. Flight procedures to get in/out are simple and do not involve any communication with Gatwick. Landing fee there will be around £20 and it's much more friendly. Opening hours are 0900-1700 in the winter, through to 1900(L)/1800Z in the Summer. It is much more friendly, there is a good restaurant and getting to London is almost as easy. You will need a taxi for the 10 minute journey to Redhill station, which will cost you £5. Trains are not quite as frequent, and it's 25-30 minutes on a fast train to London Victoria or London Bridge.
If you choose Redhill, you can follow the railway line from Dover all the way to Redhill. The longest, straightest bit of railway in the UK, which makes navigation as easy as it gets.
Hope this helps.