questions

Colouring your hair once is not so bad usually, though if your individual hairs are fine, it may be more damaging on yours than it would be on a thicker hair type.  Most people can get away with coloring a little and still keep it growing...but if you were to do something like going platinum, that'd kill it and you'd probably need to keep it trimmed at about the same rate it was growing (that's how it worked for me anyway).  When you get your roots done, don't pull it through all your hair, just do roots only (pulling it through is usually not necessary for blondes anyway, since the color doesn't fade as much as red or darker dyes).

You should leave your hair between washes as long as you can, but this varies person to person.  Doing a conditioner only wash on the days in between your shampoo washes can help you extend your time.  Many people do different things on this board where that is concerned, so you may want to read up on conditioner only and water only washes. 

Your hair needs to be trimmed to remove splits because letting those go only lets them climb up the hair.  Some people don't want to trim all their hair though, and just do search and destroy (trimming the splits off of each hair individually).  Takes lots of time but lets you keep all your growth.  If you do get an all-at-once trim, just figure out how much you want off vs. how much your hair grows per month, and make sure you don't get all your new growth cut off each time.  The average hair growth is about a half inch per month.

Mayo is an excellent moisturizer, and will work just as well for shorter hair.  The protein from the eggs in it, the vinegar, and the oils all seem to work together to make it great.  It won't make your hair grow faster, nothing does that but eating right, avoiding bad habits like too much coffee or alcohol etc, and exercising. 

Natural shampoos tend to be better, since they don't tend to have as much sulfates in them.  Sulfates are not that bad really, but they can be harsh.  If you can't find any shampoo that is sulfate free, sodium laureth sulfate is less harsh than the ammonium sulfates or the sodium lauryl sulfate.  If you don't want to worry abou tthat, you can just dilute your shampoo 50/50 or more with water, which dilutes out harshness of ingredients and still gives you good foam.  It will help you extend your time between washes too by helping your scalp adjust. 

As for conditioners, some people avoid silicones (things in ingredients that don't always, but often end in "one").  You don't need to avoid them as long as you use a clarifying shampoo once a month or so.  They'd be bad if they built up on your hair, then broke off after many months taking your hair with them, but if you clarify them off, they don't do that so they are okay in that case.