A stick can be bought fully assembled or in parts based on preference of the player. For example, some players may want a specific shaft with more or less weight based on the position they play and their strength. Also, an attack player may want a specific head laced with certain strings for more speed when shooting.
For practicing lacrosse, any comfortable work out clothing is sufficient. For competitive play their are specific uniform regulations for each level. A team will want to make sure all uniforms meet the specifications set by US Lacrosse before ordering as these specifications can change from year to year.
You can find these specifications at www.uslacrosse.org