Peter Port is an attractive town in itself, if a little spoiled by English 'holidaymakers'. The harbour is almost always full in the summer, although people visitors will be squeezed in somewhere - but you will probably find yourself in the middle of quite a large raft. It is also a very useful jumping off point for the French coast and Brittany.
The most important part of your passage plan must be the state of tide on arrival. Currents flow very strongly, and getting it wrong may cost you hours.
It is certainly possible to go from the Needles or Poole in one hop, but it will take you three tides - that is, eighteen hours. Leave at high water, and take the ebb out past the Needles. Aim to go down the Race - i.e., between Alderney and Cap de la Hague. You will encounter the flood tide mid Channel, and with reasonable boat speed (5 knots+) should arrive off Cap de la Hague at high water. Then take the ebb down to Guernsey.
From the north, there are two channels, the Little Russel and Big Russel. Both are well marked. The Little Russel takes you straight there; if you use the Big Russel, you have to go round the south of Jerthou. There are leadings lights for the Little Russel.
As you come down from Cap de la Hague or Alderney, you see Herm before you see Guernsey itself.
If you use the Little Russell, beware of cross curents near the top. If you use the Big Russel, you need to go past Herm and Jerthou. There is a S Cardinal mark below the islands, but you can turn towards PeterPort before this.
From the south or east, you merely head for St Martin's point on the SE tip of the island.
Coming from the west, you will see Les Hanois light. You can go either side of the island - the most important consideration is again the tide.
The harbour itself is tucked behind the islands of Herm and Jerthou.
The breakwater at the harbour entrance has a very obvious lighthouse, but beware of cross currents which may set you off course. Use your GPS or pick a transit to avoid being offset.
Having dodged the rocks (although the area is well marked), beware the ferries and commercial traffic using the harbour. The High Speed catamarans appear to come from nowhere if you are not looking behind you.
The outer harbour is full of moorings. Small red and green bouys guide you to the waiting pontoon for the inner harbour, or to the pontoons outside.
The pontoons in the outer harbour have water but no electricity; and are now connected to the land by a walkway, so that you no longer need to have a dinghy to get ashore. The inner harbour is tidal, and has a cill. There are lights to show when there is sufficient water, plus a tide gauge. In high season there will be harbourmaster dories to regulate traffic in and out, and they will often guide you to a berth. The inner harbour has all the facilities, but can be noisy and a sun trap. Rafting is de rigeur in either. There are, however, some finger pontoons for smaller boats (up to about 35') in the inner harbour.
Water on all pontoons, electricity in the inner harbour. Good ablutions. Plenty of chandlers. Fuel in the outer harbour, but you need to choose your moment, since there are often several boats milling around the fuel berth at any one time. in addition, the fuel berth can only be accessed from half tide onwards. Good shopping ashore.
Despite the islands to the east, the harbour is very uncomfortable in a strong easterly blow. Indeed, even in strong westerlies, the harbour is uncomfortable. The inner harbour is, of course, calm when the water is below the cill, but not at high water. The various ferries add to the wash in the harbour.