Great question, and it has distinct practical application [
] Forgive the length of the post...
For someone who can still their surface mind at will, the minimum effort is 15-20 seconds of total concentration to produce a thoughtform that has a chance to survive within the astral once the concentration is removed. If the creation is repeated often enough (10+ times daily), the thoughtform has a great potential for permanence after several weeks. When a thoughtform becomes very strong, through months of practice or through group effort (and especially when programmed to vivify itself continually) it takes on the quality of an egregore, an autonomous intelligence. This is an act of true Creation on the part of the magician, for which he is ultimately karmically responsible. However, the *strengh* of a thoughtform does not change the *density* on which it operates. Even the strongest astral egregores cannot produce physical phenomena unless they obtain and use matter of a physical/etheric density. Their usual route is to prosecute their will on the astral vehicles of humans, which once subservient can execute physical demands.
The notion of growing a thoughtform strong enough to become physical, etc is not quite correct. There is a definite process of manifestation in transforming a mental-density thought to astral form then to physical (etheric) form. At each stage, the thoughtforms can be stronger or weaker depending on the effort of the practitioner, but the devolution of the thoughtform into lower planes is separate to the strength at each level.
The mental plane is pure concepts, devoid of passion or emotional attachment. If I wanted to create a thoughtform in all three densities (which has best results) to, for example, project intimidation around me as a defensive mechanism in tight situations, or an offensive mechanism of my choosing, then I would start with the purely mental concept. This takes experience with knowing what resonates purely-mentally, and also how to trace a thought back to its fundamental concepts. In this example, it would be "I am feared" (or without the English conjunctive pecularity, simply "I-feared"). One would create this mental thoughtform by stilling the mind then thinking this thought, along with the purely-mental assocations of dominance, repulsion, power and safety. At no time would one indulge in the emotion of projecting fear, dominance, repulsion. All you are doing is creating the formative conceptual shell for the astral emotions, which in a way "implement" the mental cause you are creating.
The astral plane is emotion and more discrete thought. In this particular example, this is where the power comes from. After days of practice building the mental-density thoughtform, you would add to it the emotions of total command and power in yourself, and absolute terror and fear streaming out of you into any being in your vicinity, the sensation and knowledge that you are repelling them from any attack on you, and a supreme feeling of dominance in yourself. You would oscillate between the mental concepts and the astral emotions, strengthening each independently but at the same time joining them as a single thoughtform with dual density participation. After one or two weeks of regular practice, the thoughtform should be immediately accessible to the practitioner, requiring almost no effort to feel the full strength of the concepts and emotions. It is now his companion, available at will.
To transform this into physical (etheric) density one must bind the astral content to etheric matter. This is chiefly done through energy manipulation, condensation and then "wish impregnation" (an apt Bardon term). The most potent form of physical implementation is in your own body, so during your thoughtform practice you now add the *feeling* and sensation that total power and dominance flood your entire body, filling your head, torso, limbs, etc and every muscle, vain, bone, etc. With constant practice, your etheric body becomes saturated with this feeling. You then project this internal power outwards and make it translate as fear in all beings around you, that they involuntarily submit to your power and shrink back from you. You repeat this projection with eyes open, seeing and *knowing* that that effect is produced physically, affecting their nervous systems, clouding their mind, etc.
With repetition the mental-astral-etheric thoughtform becomes very strong and automatic. You would then bind the thoughtform to a physical movement or a word said mentally/verbally, so that it's effects are automatic when that trigger occurs. For example, you associate the presence and action of the mental-astral-etheric thoughtform to gripping your left middle finger with your right thumb and index, and from now on only vivify the thoughtform when you do that action. In time, it becomes automatic and you no longer need to add any strength to the thoughtform - its actions are immediate when you perform your action. You then go into a business negotation, or a rough neighbourhood, to test your work.
Thus, the translation from mental to astral to etheric is only possible when matter of the desired *density* is used, regardless of the strength of the thoughtform at a higher density. Humans are greatly feared among the lower astral realms because of their ability to act on all three planes simultaneously and thus use vastly more causative force than such single-density beings.
Your question about the creation of thought during projection is answered with the same mechanism. The thought is created in your astral sphere, wherever you happen to be located. If the thought is not of sufficent resonance with the sphere you are currently in, and you are focussing on it hard enough, you will be transported to a more resonant sphere. I have been in the Belief System Territories then moved to a "university" type structure on a higher astral location, and then simply through recalling the thoughts of a moment ago (BST-bound) was transported back to the same BST sphere, and through releasing them went back to the university. The only caution is that your astral environment will be subject to change based on your thoughts, especially for those skilled in total concentration, so negative emotions will place you in regions perhaps not to you liking. Regardless though, the thought you create while out of body is no different to those in-body. However, you cannot manipulate etheric matter unless you refocus on the RTZ, or go back in-body.
The example above is purely for illustration. I would never advocate projecting fear; Divine Providence would be disappointed that you had made the Universe just that little bit more negative, and your reputation in higher circles would be damaged. The same effects of safety and command could be achieved through projecting harmony, love and oneness, which Divine Providence would reward.
Also, you can condense thoughtforms into etheric matter external to you own body, such as a crystal, a plant, talismans, or the etheric body of someone else to aid in healing, security, positivity, etc. This is the basis for Bardon's "wish impregnation" in Step 1 of IIH, affecting the etheric and lower astral densities of food and water that one ingests with a particular desire.