You never mentioned what budget price you're looking to spend which could be the big deciding factor and what sort of time frame that you'd like to have it done in. If you're sold on getting a van to replace your current car, are you looking to buy new or something used..? I think either way you'd be better off to buy something stock and then converting to exactly what you want. I think that
@_WW_ had a great idea for adding headroom to your van making it more livable. Adding insulation to the inside will make staying inside more comfortable, cooler in summer and warmer for the colder temps. Were you planning to do a lot of the conversion work yourself or bring it into a shop to have it done. I'm sure there are many online shops that have cabinetry and furniture options that you could install yourself to save you some extra money for future fishing trips. More then likely you're planning to do the cooking outside as inside the van maybe problematic. Plan on getting a decent porta potty and think about where you can store it conveniently. Vans have limited space so you need to carefully work out the layout to utilize the space efficiently. For a side canopy, they even have screened-in canopies with side walls to enclose and keep the bugs out..
Given that you plan to use it for fishing trips, consider on getting a pair of 2000w or one 3500w invertor generator. The pair of 2000w generators piggy backed together would be the better choice cuz of the weight factor for picking it up to load in the van or trailer and the space needed to store them. A 3500w generator may weigh around 110lbs whereas a 2000w generator may only weigh about 50-60lbs. Wire the van up so you can plug into shore power (campgroounds) or the generators (off road)..
Good luck on your project, looking forward to what you come up with when finished..