I'm customizing a HTML template, any suggestions on plugins for good page load time?
To get the biggest improvements in page speed for your site you're going to want to do a few things server side first. The latest versions of PHP will give you a nice performance gain (https://ellislab.com/blog/entry/time-to-upgrade-php) as well as enabling g-zip on the server. From there you'll want to make sure your images are losslessly compressed. As far as EE goes there are caching techniques built in to help increase page performance. (https://docs.expressionengine.com/latest/optimization/caching.html)
As far as SEO, different people use different techniques. Some people use plugins to help them manage this, and some people do it a little more manually. If you take the manual route, you'll be creating more channel fields, but you have greater control over the content. You can also pass those fields through layout or embed tags.