My general rule of thumb is that the combined width of the braiding strips should about equal, or be just a touch over, the circumference of whatever I'm braiding around.
How many thongs you use depends on the style of braiding you're using. You don't mention what you're making, but along with u/Puzzled_Tinkerer recommendation, I also like this book for braiding advice.
So, I think back when I started (almost ten years ago? Damn, I feel old now...) I found my original instructions on leatherworker.net. I don't have it saved, but it might still be there somewhere. But here's my basic steps, and some tips.
:P Hope this helps? I tend to talk a lot about what I make.
I can point you to the same resources I went - it's all over the internet - but without doing videos it's tough to tutor online. I'm no expert & I only post the stuff I don't sell - as some of the bondage stuff, tracking via photo recognition can out people in sensitive jobs...whips making is that weird intersection of indiana jones & western culture (high morality) combined with bondage people ... it's to such an extent many whip sellers put special notes on their pages asking people who do bondage not to contact or buy from them.
You want books - if you're serious you need books.
Either of them gives good perspective - Edwards book is my recommendation - it's more comprehensible.
You will want to watch some video's ...
I have some goofy projects I've done on madidos.com ... I love testing things & rarely make the same type twice. I'm still working on categorizing & finishing most of the posts as my ADHD makes it hard to remember to photo every step.
Amending that ... Snake whip - Link - like that way more ... will say though, you can add length to the whip with several of the tricks outlined in here ... Ron Edwards Whipmaking 2nd Edition.
Basically, if you are short, back track a few passes and splice the ends together or in case of paracord - just fuse them and then resume braiding.