OK...first, lets theroze that you might need up to 150A/H's a day once you get all your toys installed. That would mean you need a house bank of 300 A/H's for a day on the hook before recharging. So 3 group 27's will give you that if you have room for a 3 battery house bank. 3 group 31's will give you about 400 AH, 2 group 4D's will give you about 300 and a single 8D will provide around 260. So...first step is to evaluate how much room you have and what will fit there that will give the capacity you need.
Standard dimensions for different battery types can be found here:
under section 7.81
I would recommend good wet cells given your intended use. Trojans would be a good choice.
Next you will need to be able to effectively charge this bank at the dock as you visit marinas which means a 60AMP range charger with three stage charging routine AND an Equalization setting so you can occasionally EQ your bank to de-sulphate.
Since you are thinking about an inverter as well, you might as well combine the charger with the inverter for wiring simplicity. The Xantrex Freedom15 will give you 1500watts AC and 75 amp charging along with echo charging for your starter battery. Other sizes are available if your needs differ appreciably from this.
The nice thing about the Freedom 15 is that you can hook in a Link 1000 to both control your Freedom15 and give you a complete rundown on battery use and status. All the Xantrex stuf can be had for less than $1000 here at the sailnet store. This is a "high road" solution, hopefully others will chime in with different thoughts about cheaper, less integrated approaches.
Note...I am specifically disagreeing with Dawg on AGM's vs. Wet cells. AGM's are NOT a cost effective solution compared with good wet cells EXCEPT in the circumstance of living aboard where they DO stand up better to constant daily cycling. Wet Cells are more cost effective for dockside use and occasional weekend/weeklong trips. His recommendation of the freedom20 and a bigger bank is fine if you want to go a bit longer without recharging and have the room.