Welcome to the forums! We are glad you are here! Good choice with your Samsung Galaxy S8+!
Having transitioned from BlackBerry to Android a few years back, I can definitely understand the feelings you are experiencing. We are here to help! I'm sure within a few days, you'll have everything figured out!
As far as texting apps, I hands-down recommend Textra. It's a great app that has a ton of customizable features - you can customize your text bubbles and bubble colours; you can set text notifications per contact (my favourite part ever); you can use a light/dark theme; and more. I recommend upgrading to the Pro version as well - the app development team are super speedy at answering client questions and troubleshoot very effectively and quickly.
I don't use any special email apps - just the stock email app that came with my phone. However, I am sure that other users here will be able to help you in that department!
With regards to other apps to download, I highly recommend Zedge. It's a free wallpaper/ringtone/notification app. If you love assigning different ringtones and text notifications for different contacts, I highly recommend it. They have everything! For example, my brother's ringtone is the 1960's Spider-Man theme song... This app is amazing.
Please feel free to post questions and to head on over to the S8+ sub-forums - they are quite active. Enjoy yourself here!