There are many suffixes that are used to create adjectives from nouns (-al, -ic, -ive, -y).
Are there any rules used to create adjectives from nouns? In example, why is the adjective excessive, and not (?)excessal, or (?)excessic?
What you are asking about is morphological productivity of English suffixes. Productivity in this sense means using morphemes to coin new words. (It just so happens my thesis deals with morphological productivity!)
There are a number of different aspects of the language system that influence productivity and the makeup of the lexicon.
As a language evolves through time, different suffixes rise in productivity and later fall in productivity. For example (from Anshen & Aronoff 1999), the suffix -ment entered into the language around 1250 according to the OED, through whole-word borrowings from French (many, if not most, suffixes enter a language this way). It converts verbs to nouns. The number of new words coined with -ment steadily rose up until around the 16th century, when it sharply began to decline. The OED cites only 2 new words since 1950 that were coined using -ment. However, once a word has been derived, and has stabilized in the lexicon, it becomes fossilized. That is to say, when we use the word "electricity", we aren't actively calculating
In other cases, two suffixes can be productive, but be restricted by phonology (that is, syllable structure and word stress). For example, the suffixes -ize and -(i)fy both are used to create verbs, but -ify is restricted to one-syllable words, two-syllable words with an unstressed final syllable ending in a vowel (with a few rare exceptions, e.g. "solidify"). For example, "glorify", "testify", "pacify". Of course, -ize is used in the other cases, so we get "revolutionize", "customize", etc. People make this choice when creating new words without even thinking about it -- one will just sound "right". This is one of the awesome things about language! Also, referring back to the above paragraph, these phonological restrictions may change over time and one suffix might take over in all new cases. (This comes from Marchard 1969.)
Many times, a suffix is chosen because it carries certain semantic features, like the suffix -er, which converts verbs to nouns, but also adds the meaning "one who does X". So another verb-to-noun suffix might be productive but doesn't carry that meaning.
Sometimes, one suffix works better in a certain situation; think of formal/informal distinctions. I might say "naivety" if I wanted to sound very formal or educated, or I might say "naiveness" in a less formal situation. Another example is that we have the word "neurological", but it is my understanding that neuroscientists often use the word "neurologic" -- the alternate word distinguishes the sense of the layman's term from the nuances of the field-specific term.
Sometimes it is unpredictable
Sometimes, a word+suffix combo gets fossilized with a certain meaning and the same word with a different suffix gets fossilized with a different meaning. Think "historical" (happened in the past) vs. "historic" (extra meaning of having a great impact on history -- can be said about present-day events). It's not -ic or -ical that is adding this extra meaning, it's that the words have fossilized in the language and then developed different nuances.
Addressing some of your examples
The word excessive was first cited at the end of the 14th century, so this is a fairly old word. The -ive suffix came from French originally. This suffix distinguishes itself from others on semantic grounds, as explained in the OED (emphasis mine):
As for the non-words, excessic/excessal/excessical, the most likely reason they were not created is because excessive was already fossilized in the language and, at least thus far, there has been no special nuance or meaning that has demanded an excessic/excessal form that would set it apart from excessive, or cause it to replace excessive. This disallowance of synonymous coinings is also sometimes called Blocking (Aronoff 1976) or the Avoid Synonymy Principle (Kiparsky 1983). It is something that is still being worked out by morphologists today.
The choice of suffix depends on what the meaning of the resulting adjective is. Different suffixes will create different meanings, some of which are nonsensical for certain words.
nonsensical is a good example:
While we're on wiktionary, the "English suffixes" category would be a good place to start digging into these meanings.
I can't be too specific about each one, but from what I've noticed, each suffix contains a bit of a meaning in itself. In some cases, more than one is possible, especially when talking about the (-ful, -less) family - in which case the one you use will depend on the meaning you wish to convey. What I gather so far on these meanings is (somewhat top-of-the-head and not nearly complete, but illustrates my point):
To say it in short words, there is no sure rule for you. Only in some cases you can guess the suffix for an adjective. Already in Latin there was an astonishing variety of suffixes for adjective formation and many of these adjectives are in the same form in French and in English. There are general meanings of these suffixes for adjectives but actually the form of an adjective is a thing of the dictionary.