I just upgraded to 2.4 and my site is taking 25 sec or longer to load with my current host even though they said they are optimized for magento to be super fast. My developers moved site to their servers and only taking 4 sec so seems like it is indeed a hosting issue. It took some doing to get Elasticsearch to work before we launched 2.4 so need hosting that will have this all configured already. Also my developer suggest Redis. Paying about $300/month for a dedicated server so want to stay in that range. Get about 30K/visits a month. Also developers say I should use AWS but not sure if this is necessary or not as this looks more expensive. Need a fully managed solution as well as I am not technical at all so need a company that has really good 24/7 support. Any suggestions?
From what you're describing in terms of needs and budgets, AWS is probably overkill. By the time you're done paying for the AWS resources plus a good management service, you'll probably find that you were better off on bare-metal. That's not the case for everyone, of course. Here's a quick read on bare metal vs. AWS for Magento: https://jetrails.com/blog/hosting-magento-aws-vs-dedicated-servers/
To support your Magento 2.4 site, including ElasticSearch, you'll indeed be best off looking at sticking with a dedicated (single-tenant) hosting environment. You may, however, find that you need to stretch your budget just a bit in order to get a fully-managed host with really good support.
What is the loading speed like before upgrading to Magento 2.4?
Do you have any caching like Varnish or LiteMage Cache in your existing server?
Is your developer running any caching system in their server?
It is definitely a good choice to run Redis but at the same time, you will also want to run a Full Page Cache (FPC) like Varnish or LiteMage Cache. Varnish is free but it is a little more complicated to setup as it doesn't support HTTPS out of the box so you will need to rely on a separate reverse proxy like Nginx. As you need to rely on another layer of reverse proxy, it is also slower than LiteMage Cache which supports HTTPS out of the box but LiteMage is part of the commercial LiteSpeed Enterprise Web Server so they do charge a licensing fee.