[DjScribbles]

I hope this doesn't come off as discouraging, but I feel like some strategic advice may be helpful. If you have any veteran teams in the area, I would strongly suggest reaching out to them as soon as possible; otherwise, you should go in search of help as soon as you get to your first event (you would be surprised how helpful your opponents can be)

While you probably could come up with a design that allows you to shift your arms in and out of the robot, it may not be a simple thing to do in a robust way. Once you get the arms spread out, you're exposing a vital part of your robot to the field and other robots. While it's unlikely anyone would intentionally try to smash your shooter, it is bound to get hit by other robots at some point.

Also, keep in mind that you will not be playing your matches alone; you'll have other alliance members that can often do the tasks that you cannot, and you are often better off doing a few things very well (ie: quickly and consistently) than being able to do everything slowly.

In this game especially, there are pretty well defined positions on the field (all 3 alliance members will not be shooting in the high goal), you can contribute as much to your team by sitting in your alliance zone receiving the ball from your human player (a catcher type design would make this really effective) and quickly rolling it out of your robot to the mid-fielder, as you can by throwing the ball into the high goal; if this is all your robot can do, but you do it really well, you would be a fantastic 2nd pick for eliminations. Even if your qualification matches suffer because you don't have a good scoring mechanism, the good teams do take notice of robots that will make a good second pick (eliminations captains will usually have good scoring mechanisms, the first pick will likely have some way to throw the ball over the truss, however the the second pick doesn't really need either of these things).

That being said, if you have the ambition and resources, you can certainly try out your mechanism idea. I would recommend trying to use pneumatics for this task, while they have quite a few draw-backs (like running out of air, added weight, limited range of motion), they are very easy to program and are extremely consistent (something to keep in mind for your next season as well).
Alternatively, you could find some inspiration in the various robot-in-3-days teams.

If you have to make a tradeoff between being able to shoot at the goal and being able to get the ball over the truss, you should probably favor the truss, both are worth 10 points, but the truss is really easy to score, and the penalty for missing is negligible in most cases. A high-goal shooter needs to be accurate, as a miss will cost a lot of time; you will likely find that more experienced teams are going to be reluctant to yield the scoring position.