Geckos are team players and don't need a lot of support around them. A CC troop such as a Morlock or Jaguar can be helpful to remove engaged enemies, something useful to any troop durable enough to survive a CC attack. An engineer can be helpful to remove isolation or adhesive but is far from required, depending on your meta. Repairing Wounds on a Manned TAG is an arguable tactic.
How you find a Gecko useful changes your composition.
If you want to take objectives or other light work early game you can use the Gecko in a second combat group with the possibility of switching groups with a command token. The small combat group can position the Gecko to take objectives and hold territory, giving it a better position later in the game.
It can also start in the first combat group. If you prefer to use a Gecko heavily in the early game to deal with mid-board enemies you will want it to be in the first group, as once you invest the orders to advance the Gecko there is rarely a reason to stop.
You can also just keep it as a stable order in combat group 1, protecting the deployment zone and only coming out in the late game to secure the final objectives. This is a viable tactic as protecting the deployment zone and final objectives are two of the most vital roles.
In a single combat group list such as in limited insertion the Gecko is usually reserved for late game objectives, deployment zone protection, and a stable order. All of these things are hard to come by in a single combat group list so the Gecko finds its niche.
Using a Gecko Duo you usually want them advancing as soon as possible. Which combat group you want them in depends on the size of your list. If you are certain you only want to advance them part way you can use the second combat group to allow for your plan in the first combat group. Most of the time they are your plan and you will want them in combat group 1.
With that many points invested you want to take advantage of their momentum, which is overkill to save for later in the game. Otherwise their composition requirements are the same. As any troop that does not have it built in, a long range specialist and smoke support can be useful to help them advance. If the Geckos are in the first combat group you want the second combat group to be based around enabling, such as the long range or smoke support suggested. An additional decent specialist can be helpful to allow the Geckos to take the easiest path instead of needing to take each objective for themselves.