Brightons our area so we know the launching really well.
The following are your options with Pros / Cons
1) Shoreham (Lady Bee Marina)
Self launch on a slip into a maintained depth marina, however the slip is at a very ackward angle (if your not used to tight launching), also car park space (free) is limited, although there is a lorry park 1/2 mile west which is £1 / day.
Launch costs are £16.50 (launch and lock) payable either at the small chandlers onsite or if the chandlers is not open to the lock keeper. Nice Tapas Bar onsite (good beer but expensive food).
The lock works on the hour going out and on the 1/2 hour coming in. So you need to get your timings right or you will be waiting another hour.
Shoreham is approx 6mile to the west of the pier. Ensure you dont go beach side of the yellow swimming buoys along the coast.
Security at Lady Bee Marina doesnt exist I would not recommend leaving your boat there overnight.
As an alternative I would leave it in Brighton Marina (1 mile from pier) , Fuel and good Bars / restaurants and good security (as these things go) contact Brighton Premier Marinas
2) Newhaven (Russell Simpson Marine) is approx 7 miles to the east of the Brighton Pier. We used to use it alot (Tractor Launch) however they are building new flats and again parking is limited.
Cost £20 (I think) however you are limited by tidal launching (any time apart from a few hours either side of LW) However they only open at around 9am and close around 5pm and the tides for the 7th show a LW at 10.55am so you would need to be there around 8am to ensure launching.
Friendly staff in Russell Simpson Marine.
Overnight in water is £10. The security is a little better than shoreham but again they are not secure pontoons so take EVERYTHING off the boat you can. Alternatively if you are back before they close they can store the boat / trailer in their compound (Ok security) Contact Russell Simpson on 01273 612612 for opening times and more details.
There is a good cafe in a portacabin next to the parade of shops, good all day breakfasts!!!
Use Russell Simpsons toilets not the public ones opposite the cafe
My choice would be Shoreham launch with Brighton Marina overnight Birth.