1. I believe pre-planning is of extreme importance for success of any serious magickal work. Minor magickal workings can be done in the flow, however without planning and preparation serious magick tends to be half baked and incomplete. Often leading to re-thinking the spell half way through then the whole process will need to be started over. In my experience, its best to think and plan before action. The same is true for mundane projects, planning produces much better results.
2. The most important magickal tool in my collection is my mind, without consciousness I wouldn't have magick. Every other tool is an extension of mind. I'll keep and use a wand for focus, a singing bowl for clearing frequency, a collection of candles for fire/candle magick, ribbons for knot magick/binding magick, a chalice for fluid/emotional magick, sage and Palo Santo for clearing, cauldron for earth/water/fire magick, a number for crystals for gathering and focusing of surrounding energy. A number of shelves filled with various books, some self written, others not, for knowledge and to alter state of mind.
3. Rehearsing a spell or ritual gives the advantage of foresight, allowing one to find out what you need before you need it. Rehearsing allows practice, making mistakes much less existent in general. It allows a ritual become comfortable and natural. I feel the rehearsal has many advantages, it's difficult to imagine the disadvantage of rehearsal. The only downside I can imagine is that you need time before hand to rehearse, if you need magick NOW there really isn't any time to practice and rehearse. But, with proper foresight you may know of 90% of the magick you'll be expected to perform and can practice beforehand.
4. I believe that the term "jack of all trades and master of none" is a limited and limiting concept, limiting the person who practices many things to be unable to master any of them. Someone who is in the habit of learning many skills, is in the habit of learning. I feel at some point (without limitations) this type of person will eventually become quite skilled at a number of arts. To define a person with a label will always be limited, a person can always outgrow any label placed upon them. I feel a possible greatness of a gold wizard (or any wizard) is mastery, but being a gold wizard does not automatically make you a master. I do think that being a gold wizard is taking a path to the mastery of interdisciplinary arts.