Can we assume that you keep the same initiative order till the end of the battle?
During encounters I will roll initiative for any NPC's or critters and ask that the first person posting rolls a Team initiative roll. The higher of the [1d6] scores will act first in my narratives. If scores are tied, I will rule on simultaneous actions with an advantage going to variables such as dexterity bonus, weapon speed factors and weapon reach or length, casting time of spells, movement distance.
As a general rule I use an order of Magic, Missile, Melee, Movement. Though this is modified by missiles that are triggered or loosed such as crossbows or pulled bows which if set may fire first in the above pattern.
Also I take into account missile weapons 'rate of fire' so an archer firing two arrows may fire one on his initiative and take the second arrow loosed as another action after the opposing side have also acted on their initiative. (Hope that makes sense).