If you have two servers, you could set one up as the database server, and one as your web server. This gives you a boost in the maximum number of users you can serve at once. If your server is reasonably powerful, it should handle 150 users without doing this (unless all 150 will be logged in at the same time).
Obviously, setting up a web application for the first time can be quite complex. Moodle isn't difficult to install, but it does need you to be familiar with how to run a web server. If you don't know much about this, you'll probably "get by", but you should do some background reading if you want to set your site up ideally and keep it secure. There's more to it than I could write here, so here's some general pointers:
Moodle 2 has much more modern system requirements. You need to install quite a few PHP modules to get Moodle 2 up and running, and you need to set your database to use UTF8. If you're using Linux, use a reasonably new distribution. CentOS is very stable and IIRC the latest version, CentOS 6, will be supported with security updates until 2017. Ubuntu is also a great distribution, and there's a lot of documentation out there. The Moodle installer shows you exactly what you need to enable on your server, so don't worry about finding the requirements before you start installing.
When you set up a database, always create a database user for Moodle, and give the user access to the Moodle database. Don't just log in using the root account. This gives you extra security if you have a lot of databases on your server. If you only have one, it's still good practice.
Always keep Moodle up to date. It's probably best to do this during quiet times, when few people are using the site.
Be strict with file permissions. It's always tempting to be lazy and set file permissions to 777 (anyone can change this file), but it's a bad idea. We've seen people's Moodles compromised because they ran a few things on the same server and their permissions were too open.
Use good passwords. Change them reasonably often.