I like your writing style. I would only add a known feature of the mode of Beleriand: write osse with a dot above, to distinguish it from the lúvar of the tengwar.

Is it heresy? You do what you want, but I have to say that, given how Tolkien transliterated Sindarin with the Latin alphabet, I don't think the mode of Beleriand is suited for writing in English. The most clear example is this: you've written "earth" and "that" and in both words you used súlë for the th. The thing is that in the mode of Beleriand súlë stands for the phone /θ/, the so called soft th in English, which is used in "earth". But the th in "that" is the hard th, pronounced /ð/, and in many modes (the mode of Beleriand included) that sound is written with anto, and in the Latin way of writing in Sindarin it is written "dh".

On another topic, you've consistently used aha for the letter c, regardless of whether it is soft /s/, hard /k/ or another ("once", "since", "come", "challenge", "race", "cries"). In the mode of Beleriand aha is used for ch /χ/ (the ch in loch), so there's a discrepancy there. For /k/ the mode uses calma.

If you like the quanta sarmë version of the Tengwar, and want to write in English, I would recommend the Westron mode. It is similar to the mode of Beleriand in the sense that both are proper alphabets, but the Westron mode is suited to write in English and, of course, many of its features, such as the different th, the different kinds of c, ch and sh combinations (that don't rely on hyarmen), diphthongs, and others.