Unfortunately the" anything goes" approach fails immediately without a particular portrayal in mind. It gets really expensive fast as well, and leads to people getting discouraged. A plain as dirt fowler might fit one context but not another, just like a short land Bess will keep you from effectively participating in early F&I events. More often than not, known historical facts about what certain people did have are available to the point of nullifying speculation. It's best to pick a portrayal first before deciding on the kit, since the known research will dictate what one needs. If you have a gun that you want to reenact with, find out what portrayals you might take on that were historically known to have the same. You'll likely find a couple, but no where near anything. Where you live and what events are within your traveling range may alter your ideas as well.
The reason so many reenactors and units suggest not purchasing any kit before being absolutely sure about what you need, is to save you a lot of money in the long run. Being patient, buying once, and only crying once is a much cheaper, satisfying, and long term sustaining strategy. Dissatisfaction is a real and constant problem as one learns and grows as a reenactor. For those that just want to make stuff up as they go, become a writer, or stick with D&D.
