All the "Cu" kana are pronounced without the 'u' bit, as です is pronounced 'des', in the proposal. As such, the ウ has to be there.
Otherwise, how would you know that シュスク is pronounced {cusku} and not {cusuku}?
ジ is pronounced {jy.} and follows the same rules as シ, as in djica: ヅジイシャ.
or ヂシャ. {tci} can unambiguously be チ, and {dji} ヂ.
It has to be that ヂ is {di}, チ is {ti}, and {tci} is ツシイ, or it would break the rest of the proposal.
For example: Is ヂクル″ {diklu} or {djiklu}?
ヲis pronounced {.y.}
To write {y'u}, use ハウ.
ハウ is most probably {xau} or {'au}.
{'u} is tricky. It would have to be distinguishable from {fu} and {xu}, and both Katakana and Hiragana have none for {'u} and {xu}. フ is actually {fu}, but you have assigned it to {fy}.
Because only フ is pronounced with the {fy.} sound, it is {fy.}. So, {fa}, {fi}, {fu},{fe}, {fo} are フア, フイ, フウ, フエ, フオ.
Since this means there is no 'hu', I decided on using ハウ to mean that. Doing a subscript ウ would be preferable. I considered ヒウ, ヘウ, and ホウ as well, and ハウ just looks the best to me.
I also considered making ヘ be {y'y} instead of {y'e}, which would mean that ハ, ヒ, and ホ aren't used at all.
ワ is pronounced {vy.}, and followed by a vowel, as in vu: ワウ.
ワ is actually {ua}. ワウ is {uau}.
The foreign {v} sound in Japanese is typically transliterated as ヴ, as in ラヴ for "love".
I didn't know that. I also have no idea how to make that symbol with a standard U.S. keyboard, so....
The reason I chose ワ for {vy.} is because we have ウア, so ワ isn't needed for it. The ウ" works for me.
The 'k' kana with º is pronounced {xy.} as in xrula: クºルウラ″ア.
That's an interesting idea. ゜ for a non-labial is never used in formal Japanese. It looks funny to the natives, so it sometimes gets used in manga for comical expressions.
{xy.} and {ky.} are closely related, and ガ, etc. are already used for {gV}, so that was my best idea. I know that's not what the maru symbolizes. (It is called maru, yes?)