Some operating systems or platforms, such as Plesk and Windows, require a licence to be purchased prior to installation. You can buy this licence from OVH, or from a reseller. You will then need to integrate it manually, through the operating system itself, or through your control panel. You can manage your licences via the control panel, under Dedicated, then Licences. In this section, you can also order licences (via the Order button on the right), or add your own SPLA Windows or SPLA SQL server licence (via the Add an SPLA licence button on the right).
DreamHost’s service gives you generous amount of resources, a few useful features, and full root access. The issue is that SSD storage is only available with the $299/month plan. The entry plan makes you slug it through with HDD, which is plain unacceptable at the end of 2019. DreamHost shones if you go for the more expensive plan but as far as cheap dedicated hosting is concerned, it falls to the bottom of the list.
Also, if your site uses more bandwidth than you’ve subscribed for, they’ll charge you for overuse. But so do most other providers. Therefore, it’s always good to keep accurate estimates of the traffic on your site. Bandwidth is not directly correlated to traffic, it depends on the simplicity and usage of your site. A simple website with 2-3 pages and with approximately 1000 visitors/mo would need around 1GB of bandwidth.