It's easy enough to trim later, but it's virtually impossible to put footage back without a visible splice. The only truly invisible splices are the ones that occur between differing shots, not in the middle of one. Be sure the first and last pieces of footage on your reel are six-foot sections of white leader. Twelve feet of leader per reel may seem excessive, but the stuff is cheap and can prevent your masterpiece from being chewed by a misthreaded or malfunctioning projector. Remember the joy of amateur filmmaking is that you can make whatever kind of film you want and edit it however you want.
Professional filmmakers have to make many compromises.
Usually, they make films that someone else has financed. Most of the time, the people holding the purse strings get the final say in what is released in theaters. In Super-8, the filmmaker almost always gets the final cut. For newcomers seeking advice, there seemingly are as many different opinions on the best method and tools for splicing as there are filmmakers. I use tape splices.