in 4/4 time i know its 4 beats per measure but, does there have to be a certain amout of measures? I always write songs in 4/4 and always use 4 measures.
No. Songs can be written in as many measures as you need. You can have an odd number of measures but as long as they each have a time signature. Some songs have more then one and change frequently. Like Metallica's "Master Of Puppets".
Ballz On Parade
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i always try to go with an even number in a phrase, for instance four bars on e or something, phrases generally last 4, 8, 12, or 16 bars but you can do whatever you want with them
in 4/4 time a whole note or crotchet makes up a quarter of the bar. divisions of a crotchet for example a quaver (or half note) semi quaver (quarter note) demi semi quaver ( eigth note) can be added. different length notes such as dotted notes can be added. however, the bar must always be a complete 4/4. if this doesnt work use a compound time signature! i.e 6/8 or 12/8 or 6 quavers a bar or 12 quavers a bar. EAZAY
listen to artists that frequently apply beat changes

Tool, Dream Theater, Metallica, King Crimson, etc

there are plenty of artists that do so