Advice on deployable IP camera system with no dedicated Wi-Fi connection

Hey! Before I get in to my post, let me just say that I am completely new here and my knowledge is probably pretty limited compared to your guys'. With that said, here's my problem...

So I work in the consumer electronics business and I have my fair share of general technology/networking/security knowledge (definitely enough to get pretty dangerous), but I need help from a true expert. To keep it short, I am in the early stages of starting a business that requires the use of an easily deployable, remote accessible, outdoor IP camera system that can operate without the use of nearby Wi-Fi. After quite a few hours of research, I have come to the conclusion that I will need a few different devices and it may even require some light fabrication, which I am totally okay with if it means all of my needs are met.

My current understanding is that I will need (work with me here):

1. A 4G LTE network gateway/modem - this will provide me with a cellular connection that will give me remote access to...
2. A PoE switch - This will provide power and a network connection to...
3. IP cameras - 2-4 cameras, self explanatory (P.S. could use a recommendation of a good camera that wont entirely break the bank)

I think this is the "backbone" of my solution but I am really at a loss when it comes to some of the specifics and intricacies of everything.

For example, is it possible/how easy is it for remote monitoring software to be installed and WHERE is it installed to? The PoE switch? Do I NEED a hard drive on site to record footage to or can I just remote monitor and use cloud storage when motion is detected (maybe throw an SD card somewhere for backup)? Is a 4G connection even remotely fast enough to upload live footage? Is it going to cost me an arm and a leg in data fees (more than $100/camera/month)? Is there software out there (to your knowledge) that will allow me to give access to a client to view the cameras for a set amount of time...say, 2 months?

I have found a few products that fit the bill, but have noticed that some cellular modems/routers seem to be VERY pricey (upwards of $600 each). Also I should mention, I have discovered cameras such as this one that would technically do everything that I am looking for, but I feel that I would be paying a ton of money per month for cellular service if I have 4-6 cameras on a site, and I am really not too certain on long-term reliability.

I am extremely grateful for any help anyone can provide and I am looking forward to responses. I am also eager to learn about how/if this solution is the right one for my use case.

Thank you again!