I do a simple round where each character does 100% of their action in initiative order. Characters can delay their entire action but not part of it. Effects apply immediately. No declaration phase. It's pretty quick.
It seems to me that you are calling on each player four times -- there are two declarations and two actions per round. That doesn't seem very streamlined. And while I like the idea of separating movement and action, in practice my players forget what they did for movement which will impact their action (less activity or pace penalties), so it's created fewer issues to just do them all at once.
I do roll initiative every round (automated) which adds a little chaos. It would resolve faster to keep the initiative order consistent through the battle (so the players always know who is next and that person can plan ahead better).
Essentially the same here.
For initiative we use the standard 2d10 (exploding 10s) + Qu bonus
There are some differences. We definitely dont bother with declared actions, even though it looks like it might allow some slight advantage to the slower actors. We have not found that to be the case in practice in nearly all instances. The faster actors tend to move and act putting slower actors on the defensive tactically. Generally speaking when an actors turn comes, they use all of their activity except that which they reserve for casting instants or some other activity which requires 20% or less, except movement.
Most movement has to used first during the action and attacks after. So you move then attack/cast spell/etc.
Interrupting Movement
If two actors are close on the initiative counter it could result in an interruption. ie PC1 decides to move (40% activity) and attack (60%) activity but V1 is only one initiative counter off from PC1, V1 can counter attack against PC1 with 60% as well for their action. If PC1 has 2+ initiative on V1 this does not occur.
Holding Actions are not Free
An Actor can choose to hold their action but they move to the next initiative counter. ie PC1 moves on 21 (rolls 9,7 and has Qu 5) but decides to hold. The next counter is V3 at 17 (rolls 4,6 and Qu 7), therefore PC1 can choose to move on 17. He could also opt to hold again and move at the next counter which is at 15. However, he cannot move between counters once he decides to hold.
If PC holds until V3 charges, he does not get to automatically go first though he does get the advantage. They both roll an d10exploding + Qu bonus + the held initiative counter points (for the holding actor) and the highest number acts first. is PC1 holds from 21 to 17 and V3 charges to attack. PC decides to attack when V3 closes, he rolls d10 + 5 (quickness) + 4 (difference from initial initiative and when he actually moved), the opponent V3 rolls d10 + 7 (Qu). This has worked very well and makes delaying both an advantage (battlefield control and observation) but risky since you could wait too late allow someone to still get an advantage on you for waiting.
Instants
we allow the casting on multiple instants in round but not non-instants. Also, no spells can be cast within 4 initiative points of another. We have not found this to be overpowering. Casting of instants breakaway from the normal activity and initiative in a couple of ways.
A player can cast an instant on their initiative counter and then hold. is PC casts shield at 21 and then chooses to hold from there. He will have 90% remaining activity. If he wants to cast another instant such as blur he cannot do so until 17 (4 initiative points later). We do allow the actor to choose to move at that time to cast the instant even if there is no initiative counter at that number (exception to the above rules of waiting until the next initiative counter).
Also instants can be cast defensively even if it is before ones initiative counter (unless a spell was cast less than 4 points prior). ie PC2 doesn't move until initiative counter 19 but is attacked by V4 on 21. PC2 can defensively cast blade turn on 21 (out of order) as a defensive instant. PC2 cannot cast another spell of any type until 17 so decides to hold when his initiative counter at 19 comes around since he cannot cast any spells and would have to wait until the next initiative counter at 15.
Fate Points
Any actor (PCs and npc/villains) can expend a fate point to move to the top of the initiative counter. Since fate points are rare (you start with a number equal to your background options and get 1 additional after a full adventure, a level up and if you do something particularly heroic), this usually only occurs in times of desperation.
For the most part, that is how we play. Generally combats move along quickly and have a dynamic flow to them. I am sure there are some other little things we do as part of combat initiative but I cannot think of them right off hand. We believe in trying to make combat go as quickly as possible.