If you have umbrellas, absolutely use them if you can! As long as the lights are bright enough to show up all, they should help fill in shadows and give that nice soft look that makes for nice portraits. You don’t have to break the bank to invest in speedlights if you’re not a hardcore “Canon” fan that can only used branded gear. 🙂 I use cheap Yongnuo speedlights: https://www.bhphotovideo.com/c/product/1101196-REG/yongnuo_yn_560iv_yn560_iv_speedlite.html They have their quirks, but they’ve worked for me so far. For the price of renting a fancy one, you can own a cheap one to use later!
Here’s some random forum posts about speedlights, wedding photography, and portraits that you might find helpful. 🙂
That’s awesome that you’re already developing “muscle memory” for the settings on your new camera. That’ll definitely come in handy during the actual photoshoot. 🙂