I'm using all the Yanfly scripts, but I think something that might be a fun addition is the random chance that an ally in your reserve party will 'jump' into the battle, cast a skill or ability that person knows, and then leave the battle. Yanfly has a script for actor variables
http://yanfly.moe/2015/12/10/yep-41-actor-variables/ which would be useful to use as the metric for their actions (if average friendship with the party is a certain amount then they have x% chance of acting in the battle). Also, could use their other variables to determine the action they take (specify for each actor a pool of skills for each characteristic and then they use a skill based on that information).
I.e. I have 4 party members and the average friendship with reserve member 1 is 50 (or whatever) and my metric is 35. So it's high enough to get some help in battle. Each turn there's a random % chance I get them to help (say 10%).
My reserve member 1 has the following traits:
Aggressive 10
Caring 30
Intelligent 10
So there is a 20% chance they use a skill under their agressive skill list, 60% chance they use a skill in their caring skill list, and 20% chance they use a skill in their intelligent skill list.
[ these could be deviced as <skill pool x: a, b, c> where X is the variable number used and a,b,c are the skills in that pool. ]
And for the Sideview system, this request is also for a visual component where the member joins the battle to act then leaves. Multiple reserve members may be able to act each turn (as long as the random % chance is true)