- Always visualize the symbols.
I think this is obvious: not everyone can visualize anything. Use what you feel comfortable with. Some people just reach out for the flavor of energy and it responds. Some need to jumpstart their abilities with memnomics. There's no one right way to channel energy. To tell people otherwise is patently ridiculous.
- You must memorize all the symbols.
I'd say you'd definitely want to be familiar enough with them to the point of being able to draw on the energies in whatever way you are most comfortable and to draw them with a minimal glance at a name list or cheatsheet if you were teaching classes, but I've been reassured that there were references (sticks with symbols carved on them, tablets, booklets, whatever) for people to research treatments, back when people had upwards of 300 of the symbols available to them...memorizing that many wasn't necessary for day-to-day use of the energies. One generally took the ones that one needed or found most useful and some of the more obscure symbols that were rarely used could be found in a library or reference work of sorts. Even at well under 100 total symbols, most of the big practitioners need a cheatsheet to help during trashpunch attunements and while teaching classes.
- It is better to wait between levels of attunement to give the body time to adjust.
This varies a lot more than is commonly accepted, especially among groups of people who are familiar with energy work. Someone who is already used to allowing energy to flow through them on a regular basis will have a much higher tolerance for how much energy can flow through them at any one time, and they will require less time between attunements for adjustment. Sometimes no time at all will be required.
- It is better to wait until Level 2 to give attunements to the symbols so that students have some time to work with the energy by itself and experience pure hands-on healing.
This is based on the assumption that the use of symbols is somehow more advanced than the use of the energy by itself. In reality, Usui introduced the symbols to his system as a form of mnemonic device... they serve as training wheels to allow you to connect to a specific frequency of the energy, or to use the energy in a particular way (it is unclear at this time which is the best metaphor to describe this). After you become familiar with the energy is really the time to move beyond symbols and connect more deeply with the energy itself. Otherwise, it's like waiting until you're an experienced cyclist to begin using training wheels. Doesn't make much sense, does it?