How can I get the donation amount radio buttons on the same line as the amount?
This layout is coming from some theme or plugin on your site.

CiviCRM includes its own CSS which delivers your desired result out of the box, and you can override or replace those CSS files. 

In this case, your site theme / some plugin is instructing the browser to lay out the form differently from how CiviCRM does per default. I'd hazard the site shown above is using a CMS theme which includes some directive like

input, label {
  width: 100%;
  clear: both;
}


You can address this by providing appropriate CSS to achieve the desired layout. Not having seen the site in question, it's hard to be more specific than that.

Anyway, here's a Stack Overflow question on how to sit radio buttons next to their labels which might help you.