Do I really need to use framework for search autocompletion and search results filtering?

I'm fairly new to web development and I have to say that I am learning it in one particular reason - to build a website where people can rate and write reviews of specific type of thing (I don't want to reveal it yet). The problem is that I want to make it as professional as possible, because I'm planning to maintain/improve the website for long time, if it's professional it's easier to do that - I guess :)

I need a search engine with auto-completion and I don't want the website to be reloaded during filtering search results. I've heard of Ajax, but I'm not sure how to bite it. I can make use of HTML/CSS and PHP, however I'm not an expert.

1. What technologies are best to achieve that? Any libraries/frameworks?
2. Do I really need theses frameworks? Can I do it in vanilla PHP/JS?
3. Maybe the whole website should be build using a particular technology/framework? Will it simplify upgrades? Should I only go for front-end/back-end(PHP) framework only or both?