I am done with this now. Capital letters are not normally used, and look mostly like bigger versions of the lower-case letters, so I dropped them. They are in a separate font file anyhow, so the traditional way to use them is to create a document in lower (normal) case, then add Upper case letters to the first letter of a page/paragraph, or for Proper nouns.
With that out of the way, the attached layout would be implemented by a TrueType font plus something like AutoHotKey. The result is that typing phonetically results in correct English to Sindarin as defined by Tolkein in Appendix E of the "Lord of the Rings".
All the normal and abnormal characters are on the keyboard, so using modifiers is not needed. However, for the purist I have included all 14 modifiers, each of which places itself over the prior letter so no AltGr gymnastics are required. Also, I have included the entire base -12 number set on the top row.
To use:
Consonants and vowels are typed normally. Shift makes vowels long and control adds a y to the end of the vowel. Shift adds an h to consonants, with the exception of shift-n which makes an "ñ". Control-n makes the "ng" character. Typing a letter and then a modifier (above the numbers) places the modifier under, over, or next to the letter automatically.
100% of this can be done on the 1x1 keycaps, but just to show how it looked I transliterated the mod keys into Tengwar.
If someone actually wants to do something with all of this, let me know and I'll provide you with source material.
Enjoy!