The answer to your first question is, yes there is, sort of; the answer to the second is, sometimes it’s easier than others. Let me explain. Some suffixes that are used to form adjectives from nouns have very clear meanings. An example of this is one of the suffixes you give, -like. When –like is added to a noun, it forms an adjective that means ‘like the noun’: so birdlike means looking, sounding or behaving like a bird, and childlike means looking like, behaving like or similar to a child:

Although their birdlike calls were common, the creatures themselves were keeping well out of sight.

Tom was waiting for Ania with a red rose in his hand and an expression of childlike excitement on his face.

So, if you wanted to say that someone reminded you of a bird, you could venture to guess that the adjective you’d need is birdlike, and in this case you would be right. However, -like is also used to form adjectives whose connection to the noun is less direct; a lifelike picture, for example, is not exactly a picture that is ‘like life’, but rather a picture that realistically resembles the person or thing it represents. The suffix –ful is similarly straightforward: it is used to form adjectives that mean ‘full of the noun’, such as fearful or joyful.

Other suffixes used to form nouns are more complicated. The suffix –ish, for example, is used to form adjectives that mean ‘resembling’ or ‘typical of’ the noun:

For a moment Jack’s smile had a wolfish quality to it.

Sometimes, however, the same adjective can have different, even contradictory meanings. So childish means ‘like a child’, but this can be in a good way (as with childlike) or in a bad way.

My return to Cork was an effort to get in touch with some of that childish innocence.

You could also come into contact with a childish tantrum - though not necessarily from a child!

Some suffixes are used to create words with even more varied meanings. –y is added to all kinds of nouns to form adjectives with a wide range of meanings, often several different meanings for the same adjective. So fishy can mean ‘smelling of fish’, or ‘tasting like or of fish’, or ‘looking like a fish’; but it can also mean ‘arousing suspicion’. A girly person is very feminine, but a girly magazine contains pictures of naked women, while a girly film is enjoyed mainly by women and a girly night out is for women only.

I think this is enough to show that, while some suffixes used to form nouns from adjectives are predictable, others are not. You can have a stab at adding a suffix and in some cases you will more than likely get it right, especially if the adjective you want to create means ‘resembling the noun’. However, you can’t be sure that the adjective you have created really exists, or that it has the meaning you think it does. Your Macmillan English Dictionary will give you some help on this subject, as it has entries for some of the most frequent suffixes, including –like and –ish.

To answer your first question, I would say that United States is acting as a modifier here. Although it is a noun itself, in this case its job is to give more information about another noun; this means it's behaving like an adjective and as a result, it doesn’t require the possessive apostrophe. Contrast this with the example below, where the United States is behaving as a noun:

Opposition to the war within the Labour Party and among the British general public meant that the Wilson government could not satisfy the United States' desire for support.

A similar case would be the United Kingdom: you would say the United Kingdom government, not the United Kingdom’s government. You can’t do this with most country names however – you don’t refer to the Denmark Prime Minister or the Italy government, but use the nationality adjectives instead (the Danish Prime Minister / Italian government), although you can, of course, say Denmark’s Prime Minister or Italy’s government. Other country names that can be used in a similar way to the United Kingdom include New Zealand and the Netherlands.

As for the second query, it simply means from the start. This is one of the very many idioms drawn from sport; at the start of a race, the starter traditionally says: ‘Ready. Steady. Go!’ or some variant of this, such as ‘On your marks. Get set. Go!’ The word go is the signal to the athletes to start running, so from the word go simply means from the very beginning.