To replace the back glass it’s necessary to remove the front screen?

The decision to remove the front glass is entirely up to you; the repair can be done either way, but there are trade-offs to each decision.

First off, removing the screen itself doesn't help or hurt the repair of the rear glass; rather, it just clears the way for you to remove other components that could be damaged during the repair.

It's my understanding that most of the DIY replacements are done without opening up the phone, and most of them are successful. There are, however, occasional issues that happen as a result of trying to replace that glass. The thing is, Apple uses really strong glue to hold that glass onto the back side of the phone. So getting the glass off usually involves heating it up to a pretty high temperature in order to soften the adhesive and allow you to remove the glass it's holding in place. The necessary temperature can and occasionally does damage internal components of the phone; sometimes it's a part like a camera that stops working and other times it'll be a flex cable that gets damaged and needs to be replaced.

The professional shops who do glass replacement use a precision laser that is programmed to only burn the adhesive off the parts of the glass that has it. The duration of the laser is very brief, so it tends to not transfer much heat to the interior components of the phone and thus lessens the chance of damage. If you do it yourself, you'll almost certainly be using a heat gun to blast the entire back of the phone and get it hot enough to get that glass off.

Another area of caution is the wireless charging coil. It's exposed through an opening in the rear of the case and can easily be cut or damaged as you're chipping away at the rest of the glass. Note that there's no glue on the glass behind the coil, so you won't be working on that part of the glass since it's not stuck down.

Given the chance of damage, the only way to be 100% sure you won't ruin something inside is to open the phone up and gut it; remove everything from the inside before doing the glass replacement. Naturally that has a lot of downsides to it as well. First, the very process of removing all those parts has its own risks; there's always a chance of damage when taking things out that are glued down. Also, if you're going that far in taking everything out, why not just buy a new housing and put everything back into that? So yeah, that's not an option that most people subscribe to.

To be honest if it was me I'd seriously consider taking a few items out. In particular the non-replaceable front camera assembly and the battery would be two things I'd want to protect. The front camera assembly because as part of the Face ID system if it's damaged it can't be replaced except by Apple. The battery simply because heat is the enemy of batteries so I'd want to have it out to avoid the possibility of damage to it.

If you go that far, I'd suggest you might as well pull the rear cameras just to be safe and keep glass from getting in them.

I realize you've already ordered your glass, but you should be aware there are two different kinds you can get. You see, the camera lens bezel actually overlaps the glass, as it's put on after the glass and welded in place, so it helps secure the glass too. So when you're chipping the glass away, you'll need to make sure and get the glass under the lip of the bezel out.

Anyway, back to my point; you can buy a glass that is sized exactly the same as the original glass, but that means the camera bezel has to be removed since the glass won't fit over it. You can get it out with a chisel or a Dremel or some other means, but you'll be left with figuring out how to resecure it since none of us have that little micro spot welder Apple uses.

The other, much more common, kind of glass has the camera bezel hole enlarged so that it fits over the lip of the bezel so you don't have to take the bezel off. Of course that means there's a gap between the glass and the walls of the bezel; it's not a lot, but I'd think you'd want to maybe use some silicone sealant or something to make sure you don't leave a path for water to get inside the phone.

Okay, those are my thoughts and ideas regarding rear glass replacement. I've looked carefully at it for a couple of phones but haven't actually done it myself, so take them as my (informed) opinions rather than cold hard facts. I've generally opted to go with replacing the complete housing, especially in one case where the frame was bent and a straight glass replacement wouldn't have worked anyway.

Good luck; let us know what you decide to do and how it goes!