I know this is a bit late. Didn't see this thread before.
Most of what I do is scripted game news (this helps with SEO too as you can load the script as captions). I will attempt to impart what I can.
When doing a read, I don't feel it's necessary to memorize it. Most script reading for broadcasting (radio, etc.) is done with no prior knowledge of the script. You already know the content because you wrote it, that should be sufficient.
Record the full thing. You can do this in multiple takes. Perhaps just record a small paragraph at a time. Editing these together afterwards is as simple as cutting out silence.
As you go along, you will encounter stumbling blocks. Words or phrase combinations that sound wierd or are hard to pronounce in tandem with one another. Edit these as you find them, you won't remember them all later.
Practice breathing from the diaphragm. The easiest test for this is when you breath in. Your stomach expands out, but your shoulders don't move. If your shoulders move, you're doing it wrong. This allows for a greater amount of air in the lungs and thus a longer time before you have to take another breath, meaning more words.
You cannot get a good feel for pacing until it has been recorded. Also, ensure you're not equating pacing with speed, but consider that increasing the speed can impact the pacing as it lessens the duration of less exciting segments.
Once you've recorded the whole thing, listen back to it 4-5 times. Keep notepad open so you can note where there are weak parts in the script, parts that are boring or don't flow well.
Make adjustments to the script and then record it again.
As time goes along, you will get better and be able to gauge the pacing from just the written word. You'll also know exactly how long you have to write for a particular length of video. For example, my series Feature Creep is fairly rapid. The speed equates to 1 full page, Calibri font size 1 in MS Word and will get me 2 minutes and 30 - 45 seconds, leaving just enough room for intro/outro.