You'll want to consider this from all aspects, Mr. Purchasing Manager.
If you read this thread, you'll find there's more than just purchasing the equipment "right" to make you a happily satisfied customer. Suprising Response trying to find electronics guy in Ft. Lauderdale
Of course, if you're going to install the gear yourself and are comfortable in dealing with whomever you buy it from in terms of warranty and availability of installation and tuning advise, you can purchase the gear anywhere.
Otherwise, the reputation of the dealer or marina you end up working with becomes paramount. Once you find one you're confident in, you'll benefit from their advise and expertise as they'll be the one's standing behind the gear and the work.
The individual wants and needs of boat owners are so varied that any boat sitting at a dealership is likely to be either bare-bones equipped or fully outfitted with nothing much in between the two boats.
I'd talk with as many people as you can with similar boats to find out what has worked well for them. Have fun, it's time-consuming but still a lot of fun as it's your boat!