Is Vietnamese a tough language to learn?  

If you can aim it , then you can do it. Just don't stop and one day you'll ace it. Take help from youtube.

many of the words are like 2-5 characters long. But it's hard to pronounce. Writing without the tones is easy but speaking the language is difficult.

I've tried my hand at learning as well. I know a few key phrases and questions, but that's all I know currently. I am hopefully to keep learning though. It's just going to take a while for me. 

You can take lessons from here. 

I've been taking a lot more lessons with the pandemic looming around. I figure with all this free time, I can go ahead and just keep learning. By the time this all ends, I'll be fluent in Vietnamese! :)