I think @joeyk wrote a good answer and comprehensive article here.
There are hundreds of ESP’s out there with shared IP’s or dedicated IP’s. At the end of the day it comes down to what is outlined in that article.
If you are looking for mass mailing off the bat - you might want to look at setting up multiple IP’s with a system or go for those big mass mailers, trying to do it immediately with AWS /Sendgrid or the likes will probably get you shut down pretty quickly.
Start off slow and with your best data, stuff you know how opened, practise “warm up” even on shared IP’s so the ESP gets to know you and flags you as okay.
Clean your data, I personally use a more technical (less user friendly service) https://veribounce.com. I also use SendGrid for my mailing and I mail in excess of 1M+ per month (but it took me a while to get there).