You mentioned putting together a 5's team so I assume you are looking for these answers when working on a pre-made team instead of Solo Queue. I am going to assume that you can communicate by talking instead of typing, if you can't, get some sort of voice communication.
Baller Shot Caller
Anyone on your team can be the shot caller, regardless of role. Shot calling is less about role and more about having game knowledge, being able to judge situations based on team strengths, and there must be team cohesion. If the shot caller makes a call and nobody follows it, then you will never know if that call would have worked or not. The team has to trust the shot callers judgement.
That said, the shot caller should not be the only person providing information. Your team should be telling you things like "Flash is up", "Top no summs", "I am huge right now", etc... Shot callers are very good for having a default leader for when situations arise. Just took towers and half the team is wandering around? Shot caller give us your guidance. What is our plan leader? The enemy trying to pressure an objective? How do we react? What do we do? Tell us shot caller.
Also, record your games. It is easy for teams to get distracted and side tracked debating what play should have been made, what could have been done, etc... This all isn't really important during the game. If the enemy team got dragon then they got dragon. Figuring out the perfect play does not erase that fact. Plan accordingly. Helpful input on how to deal with the situation going forward is good, but discussing what micro play went wrong letting the enemy take dragon (or whatever is being debated) can be saved for the review. Gameplay reviews are a great time for everyone to be heard. This is also a good time to call out when bad shot calls were made. The important thing is that the team focus on the game and follow whoever they designate as shot caller. If the person has made a series of bad calls and isn't really good at shot calling then fine! You can figure this out in reviews and then a new shot caller that the team still trusts to follow can give it a try.
To push or not to push
I have a general rule for bot lane. Generally I do this :
- Let the ADC/Marksman control the wave
- Let the support control the engages/aggression.
Your adc should be able to control the wave. They can just last hit, they can continuously auto attack to push, etc... You mention that your team is bronze/silver. If your adc cannot control the wave they need to learn how to in order to improve. Also, if your adc needs help pushing the wave (maybe they want to push and go back to buy) on voice comms they can just tell you to help them push. Solo queue they can also ping the turret so you know to hard push. Remember that if you do end up taking farm it is not a huge deal unless your adc says something like "I need all of these minions to get my (insert item X)". But the main point of pushing to go back is so that the wave will reset. Don't just steal the last hits from your adc, but the idea is to push the lane as fast as you can and get home. As you both improve you will be able to do this fast AND not miss farm while doing it. So in a pre-made, have the adc tell you when they need help pushing.
As for when to push, it really depends. You have to think about what pushing and wave control accomplish. A few basics:
pushing
forces the opponents under turret. This is usually done in the hopes that the enemy adc will miss lots of cs. This works really well at lower levels, but part of being an adc is learning how to last hit under turret. The other reason is so that your jungler can assist in diving the enemy under their turret. This is usually done by building up a large wave and then pushing fast to the enemy turret. This makes it hard for the opponents to fight back, as they will draw aggro from this huge minion wave.
freezing
Freezing a minion wave is locking the wave in a position so that the enemy wave has more creeps than your incoming wave, meaning it will kill your wave faster, meaning your wave will no longer push towards their turret. Generally you try to freeze the wave just outside of your turret so that you can safely farm the enemy wave. The downside to this is that if the enemy is stronger it is easy for the enemy to break the freeze and force the wave into your turret. This also makes you a potential dive target.
zoning
Zoning is done as a more controlled way to try and punish the enemy. Zoning an enemy means trying to keep them out of experience and farming range. Usually this is done by placing the support and adc between the minions and the enemy laners. This is generally done when you have a decent item or health advantage. The second advantage to this is that is gives you a good chance to attack the enemy if they try to compete for farm, giving you a chance to kill them without having to have the jungler come dive. The disadvantage is that this leaves you in a spot where you can be vulnerable to a gank, although the enemy lane should not be strong enough to contest you so you should only be in the position where you have to back off instead of getting killed in a gank.
These are very basics to wave control and laning, but they should give you (and your lanemate) a basis for knowing what to do with the wave based on how you want to combat your opponents.
Hope this makes sense / helps!