Go ahead and get what you think will work, just to start with. Chances are pretty good you will change your mind regarding what you really want once you get some trigger time on whatever 870 you start with. That is not a poke at you or your thread, or an attempted insult, I mean it sincerely and I pretty much know the feeling myself. I have been mixing and matching with 870s for about 30 years now and am still playing with them. You can buy, sell, swap and trade till you get exactly what suits you, and if you shop and trade carefully you will never lose a dime in the process.
I tell people often to try whatever it is they are thinking about 'in the flesh' to see if they really like it- sometimes you have to buy it to try it, but if you can get hands on one belonging to a friend you are that much better off. With 870s their modular nature and wide variety of barrels and accessories make it possible to get pretty much whatever you want. But it is ice to be able to 'try before you buy' and shooting friends' or acquaintances' guns will let you do that.
Friend Dave McC has another saying, that 870s may not reproduce but they DO multiply. It seems that way. Once you get started you always seem to run across a bargain on this gun or that barrel or some other accessory item. You get exposed to ideas you never thought about and some of them you will want to try. There is absolutely nothing wrong with the process as long as you are _shooting_ whatever it is you are experimenting with.
Since the 'tacticool shotgun' became popular I see more and more folk who simply MUST have their gun "finished" with all the accessories and bolt-ons and gunsmithing in place before they will even fire a single round out of it. I secretly wonder if even then some of these folk actually shoot them, once they get everything they want bolted on. It's a mystery to me, for sure, since to me a shotgun has always been the most utilitarian of guns, the gun everyone had one of, the gun everybody used.
I know how much fun the anticipation of a new project is, believe me. But don't let that stand in the way of accomplishing the project. Nothing says you have to get it absolutely perfect the first time out the gate.
lpl/nc