I think that most artisans (of any level) have ridden high on this tide at some point in their creative lives. Unfortunately, I can say that without an abundance of planning that many multi-level projects can fail before they even have a chance to be fully explored. Though I am indeed speaking from my own experience on this matter, I also have witnessed the great ideas of others fall by the wayside (on more than one occasion). So eager are we to plunge into the act of creating, that crucial things are often missed. These omissions in the planning process often lead to a waste of time, effort and money and result in frustration that can dissuade future growth.
I am not saying that every thought or plan should be belabored to the point where all interest is lost, but having even a small bit of planning in advance can result in a road map that will give a clear vision of what skills, material and time you would need to finish a given project. Beyond that technical planning aspect, understanding that everything is truly a learning experience is something that should also be a given in a creative work. Not every project will end in a satisfactory manner, but one will have learned how to better accomplish the goal when the endeavor is revisited.
One project that I often see historical recreationists start, and then quickly flounder on, is the "I am going to spin, weave and sew my own dress from scratch". For most individuals, that is a better long term goal than it is an immediate one, as they are not even starting with the requisite skills needed to bring the idea to fruition. (Note that I use this specific example because it is one that I see come up frequently, and I typically see two things happen after the excited individuals publicly announce their project. The most common is that once they actually begin their research they become so overwhelmed by what they now realize they do not know, that they are discouraged from further involvement with the project or they manage to make a meager a start and then discover that the time necessary to bring the item to from dream to reality is so vast that they are deterred from moving forward. Those who, perhaps, lose the most are those who also invested a great deal of money in materials before they even have an understanding of the skill needed to manipulate them.)
I personally think the ideal progression of that particular concept would be to research and learn the specific garment in question first. Learn the patterning, learn the most economical ways to cut the cloth, learn the essential methods for sewing that specific garment and made several such garments out of purchased fabric. Knowing exactly how much fabric, of varying widths, one will need to complete that dress will assist in weaving enough yardage when the time comes. Additionally, learning the proper hand-stitches for the garment in advance will make for a finer execution on the final project.
While exploring the sewing side of a project of this scope, it is a simple thing to purchase an inexpensive drop-spindle and some wool and begin the process of learning to spin (many SCA groups have fibre arts guilds or experts who are more than willing to coach a newcomer into this art). Even badly spun yarn may make for a decent weft, but to spin yarn that will hold up to being warp is a more intricate task. Remember too, that just to practice spinning is not enough, one also needs an understanding of the type of textile of which the historic example is comprised, how fine was the yarn? What type of spin was employed? What direction was the twist? A thick, soft, woolen spun yarn with a Z twist would be useless in trying to recreate a gown that was a fine worsted with an S twist.
And of course, there is the art of weaving that needs to also be addressed. There should be an exploration of looms (again, a local fibre arts guild can come in handy). Will one be purchasing a loom? Making one? Warp-weighted looms are not complex structures and inexpensive to make, but if the end goal is to use one in the creation of a gown (on which countless hours were already spent spinning), then before the project is started there should be a understanding of weaving, of how it was done historically and of how to calculate the necessary amount of yarn is needed for a project so that there is little waste. Weaving test pieces in advance is so highly recommended that I would say it is a "must do". What if your hand spun wool does not hold up as warp? What if the wet-finishing process warps the fabric because the spin technique was so rough that the cloth puckers and will not lay flat for cutting? (The included photo shows commercial warp and handspun from my early spinning days. The spinning is somewhat consistent in terms of grist, but amount of twist varies far too much and wet-finishing caused it to pucker up like some form of tragic seersucker. I may yet iron this textile into submission, but I am very glad I made this mistake early on and well before I attempt something on a much larger scale.)
I will be the first to admit that I initially rebelled at weaving samples, and I have a definite preference to make use of everything I create. So in the process of learning to spin, I have made a good deal of yarn that I am going to use (or have used) as weft in mats, pouches or rugs (all things I have created while learning the process of weaving). Just because it is a sample or created in the process of practicing an art does not mean that it is a waste of time in terms of material results! Sample away and enjoy the actual process of learning a new skill!
Understand that it is not my intent with this post to discourage anyone from developing epic plans for projects. (Indeed, I am sure that someone out there has gone straight from notion to handcrafted gown with little in the way of samples or sidetracking. I do think that those people are minority and likely very exceptional individuals.) I think that grand goals are something on which artisans can thrive, but I do believe that taking smaller steps on that pathway are more likely to result in actuattaining the final destination.