You've asked some big questions, and unfortunately there are no easy answers...The 12 and 14 PAs are similar but very different, if that makes any sense
There are pros and cons with each. If you look, there is a thread or two on this forum where owners of both !2 and 14s compare them to each other. You'll get some answers there that will help you decide, because its hard to make a good decision if you don't know what questions to ask 
I would recommend taking a look at both, and test driving them at a local dealer's demo day if possible. Both PAs are suited to lakes or ocean...
When I bought my PA-14 I didn't test drive it first, or have any accessories when I took my first trip out on the water to go fishing. It performed great, other than a steering issue that Hobie later fixed and made available for all the PAs. The PA is a great fishing platform, even without adding accessories that aren't included with a new PA. Once you've decided on which PA you want (12 or 14), I would recommend just going out with nothing other than what you'd normally take on a fishing trip (rod & reel, bait and/or tackle, safety gear, maybe something to eat & drink, etc..). Then afterwards, think about what would be nice to have added to the PA to make the fishing experience more enjoyable, a must-have for you, or safer, etc...You don't have to buy or accessorize before your first trip out. The PA has everything you need to get started. As time passes you'll probably browse many kayak fishing websites lookiing at different accessories and you'll get many ideas to customize your PA...And with each new idea, you'll have questions...Thats why a forum like Hobie's is so great. Guaranteed...Whatever the situation, problem, or experience... Someone on this forum can relate and will help you.
