PS I know London very very well, I live and work there and my job takes me all over London each and every day.
A couple of points to consider.
Do not book hotels near CrossRail construction as whilst they limit noise there will be disruption until 2018, so avoid Tottenham Court Road, Bond Street, Paddington, Farringdon.
Dover is about 80 miles from Central London, and the same from the nearest main hub airport of Gatwick, it's a 100 miles from our main London airport Heathrow.
DCL did as you see put on coaches and many people preferred these for connivance, they however were very expensive.
I drove there I live 75 miles away by direct route. There is a small car hire place but a walk from the terminal, see later, and couldn't cope with many people requesting cars or dropping off.
The main alternative route is by train from Central London.
The very fast service to Dover Priory is from London ST Pancras which is next to Kings Cross to the North of Central London and is by high speed train using the channel tunnel rail link for half the way, you can go by normal fast train from London Bridge, Victoria, or Waterloo East but take care some trains of SSY eight cars split into two four car trains at Faversham
All these trains are operated by SouthEastern rail and are good sized trains but avoid hush hours, the high speed St Pancras route costs more and if say your going to then travel by tube you may find it longer.
.it takes an hour but Dover a Priory is not next to the harbour, and the port pier is a long walk down a narrow road over bridges and it has large trucks on it.
So a taxi from the station is advised.
This is why so many choose the DCL bus or organise private transfers as these pull up at the terminal and avoid rush hours, pulling bags on and off trains and into taxis or tubes either end.
Gatwick is to the dough of London do a direct private transfer avoids London. Whilst Heathrow is west London both airports are connected by motorway ( freeway) using M20 M25 and for Gatwick M23.
The famous white cliffs of Dover are port side, East of the Ship, and there is the famous Dover a Castle there as well with stunning views.
I would suggest fly into Gatwick or Heathrow get a train to Central a London stay a few days in the Victoria area sightsee, then either private transfer or train to Dover.
Check in was normal but in a small confined space and so they will stick to PATS there, the terminal is on two floors so slightly bigger than it looks, border control quick, it has a good cafe in it, but you can't really leave again to tour the town without a good walk or a taxi and the road is a commercial truck access route.
I have walked it when we took these photos and not on that cruise and I saw people try to walk it with luggage a in both directions and I would say don't.
The English Channel has high movements in tides and so as the photos show be prepared to walk up steep steps.
You get off fast at Dover but with an hour to any good airport and strict security do not book anything before 1pm, and note one cruise in 2010 changed it's arrival time to 10.30 due to tides.
Some points
Check SouthEastern Train services for any planned engineering work about three months before travel.
London Bridge is having a major infer structure change and can be closed on weekends up to 2018. Its also just beneath the new Shard building the highest in London.