While I agree with the sentiments of Bert and Pixie, the following rambling may just be of some assistance.
1. I don't know anything about SVQs and I suspect the same goes for a number of people on AnswerBank. Therefore, and this is part of the answer to your first point, it might have helped those of us who are prepared to help you if you had explained what an SVQ is. I am assuming that the abbreviation refers to Scottish Vocational Qualification.
Thus, to answer your first point, it is important to use clear and concise language that does not assume any prior knowledge in your readers of the subject about which you are writing.
2. The second point, significance and potential risks involved in committing a communication to a permanent record, might best be answered by emphasising the absolute need for accuracy in any statement that is going to be preserved for posterity. Put another way, if something is on permanent record - however that record is kept, (on paper or recorded electronically) - it will always be "retrievable" and if it contains any inaccuracies, these may well come back to bite you at a later date.
3. //The effect of style and tone on the reader...// In other words, know your audience or readership. If you are writing a fomal letter, to a prospective employer, for example, the style of writing and the tone of the letter would be dramatically different from the sort of thing that you would write to your best mate. Similarly, an email, while reasonably containing certain abbreviations, should follow established etiquette and may well be less formal than a written letter. At the end of the list of course would be the style of a text message (or txtmsg) where all sorts of obscure and sometimes complicated abbreviations are used and accepted by ones peers (Example "CUl8r m8") but should never be used in formal communications to either your elders or superiors (imho).
4. You may well know your subject inside out but it is always poosible that this knowledge is not shared by the person to whom you are writing. I'm thinking here about jargon. All trades, industries and professions have their own jargon which is well understood by those in that trade, industry or profession. This jargon will probably not be understood by outsiders and therefore this should be avoided lest it alienates the reader. Just because you understand what you're saying it doesn't mean that everybody else does!
5. Confidentiality. Although you may mark a document as "Private" or "Confidential" or "Personal" you will have no guarantee that the recipient will treat it as such. With emails and other electronic communications there is always a danger that you - or the recipient - will press a wrong button and forward a document to everyone on a mailing list. ("Reply All" instead of "Reply to Sender")
Whether or not the above comments are of any use to you, it would be appreciated if you could take the time and trouble to at least acknowledge our efforrts!
Good luck in your endeavours.