I'm hoping that this is a simple question concerning the setting up of a database

I am wanting to create a website where subscribers can log in and then perform roughly a half dozen searches. I know that the information that will be downloaded daily to the database will be in hml format. My question for you are as follows:

1) The database that I need to build, for simplicity sake, will allow the subscribers to search for very basic information such as "Do they own a dog" and then the answer box will populate as a simple yes or no. Or the box may pull the name of the person being searched town. Are there differing types of databases to choose from? I want it all to be automated so the places we download from will automatically download every evening.

2) How does one tie a database to a website?

3) This database will have millions of records within it but again, each record will only have half a dozen pieces of basic information. No pictures or anything other than data. What size server can handle both the amount of this information as well as the potential for thousands of people accessing it all at once?

4) Lastly, is there a provider that you would recommend me reaching out to in order to set all of this up?

Thank you in advance for your help!