First of all, several of the vowel letters have multiple values (e.g. /y/, /ɯ/ and /ɨ/ for y). Your "rules of sound" should explain under what conditions one of these values is used and not the other. By the way, I'm not even sure if these value represent distinct phonemes or only allophones. (And if you don't know what those terms mean, you should look them up.) The convention is that letters between /slashes/ represent phonemes and those between [brackets] are phones, but in your post you use slashes for the unreleased allophones of ć, k, p, and t.
Second, the alphabet in general seems geared to making maximum use of diacritics rather than ease of use. Why, for instance, ł for /w/ when w is free? The reason ł represents /w/ in Polish is that up until a very recent sound change, this letter was pronounced [ɫ] (a velarized alveolar lateral approximant)--and, in any case, w was already in use for [v].
Third, you need to tighten up your rules for geminates (double sounds). It beggars belief that every sound in your inventory can be both long and short. Take ŗŗ, for instance. I've never heard of any language that contrasts /ɹ/ and /ɹ:/. On the other hand, it's very common for a contrast of /r/ and /r:/ to be realised in some other way than [r] vs. [r:]. Many languages (e.g. Spanish, Basque, Albanian) have [ɾ] (an alveolar tap) vs. [r] (a trill), for instance. With that in mind, r /ɹ/ vs. rr /r/ makes a great deal more sense than what you have (and dispenses with another pesky diacritic!).
Fourth, you need to take more about syllable structure. You say that complex consonant clusters don't exist, but you don't mention if there are any restrictions on where the two-consonant combinations occur, let alone what consonants they involve. For instance, is ktorr a possible word in your language? What about člogđ? Nothing in your rules as written forbids these.
That's probably enough for now. Let me know if you have any questions.
1. The /y/, /ɯ/ and /ɨ/ for Y are allophones. I haven't decided the conditions where one of the values are used and not the other, yet.
2. Ł is used for /w/ instead of W because I choose to have it that way. W is only used in loanwords.
3. Every sound in my inventory can
be both long and short (except for H, I just realized it wouldn't make sense to have H be both long and short). Look at the Finnish and Japanese language, most of their letters (or sounds I should say in the case of the Japanese) can be long and short.
4. C, Ć, Č, Đ, H, X, and Ź aren't allowed in two-consonant combinations.