Well, that's where it really depends on the setup your band is using. If you want to be able to hear the whole band in your IEMs, you'll need a way to send mixes to your transmitters. Depending on the venue, the engineer may be able to send individual mixes back to you just like they would for normal monitors, so all you would need in that instance is to send your main LR to them and then go through the normal process of "a little more of this, a little less of that," et cetera.
The way my setup works, we have our transmitters mounted in a rack case along with a digital mixer (Behringer XR16) and two ART S8 mic splitters. We run all of the instruments and microphones to our rack first, then the signals get split by the S8 units, and we can control individual mixes on the AUX outputs from iPads while sending unaffected signals to the FOH. This gives us two huge advantages: each person can easily control and adjust their own mix (which makes the FOH engineer very happy, as it's way less work for them), and the signal sent to the main board is completely independent of whatever we do in our ears. For example, if we want to add a slight reverb to our vocals (which can be helpful for singers getting used to IEMs), the engineer still gets a dry signal and can add his own effects that are appropriate for the venue.
Do you know how your band plans to tackle the IEM setup? Is each member going to have an individual transmitter and receiver? Will you be sharing mixes? If you're doing it the way I do, it's a serious rabbit hole to go down, as you're essentially becoming your own monitor engineers; however, it's super worth the time and investment in my opinion.