I don't think there is really any benefit in having a Samsung tablet and smartphone unless you really like TouchWiz. The two don't magically sync between one another so it's not like having multiple Apple devices with a single Apple ID. Nope, get whichever tablet works best for you. Look at the features, performance, OS (and if it will be upgraded), and price. I ended up with a Samsung Galaxy Tab Pro 8.4 because I wanted a small tablet that I could use while laying down in bed. It just so happened to be a Samsung tablet as, at the time, it was going for $200 new at Best Buy. It came with Android 4.4.4, has a great screen, and it supports microSDXC cards. The battery life could be better but like I said, I was really only looking for something to use before I go to bed.
My primary tablet, and machine, is a Surface Pro 2 though. It doesn't slowdown or get buggy when I have more than one app running, the stylus is superb, and it runs any program that I want. Then again, it's in a different class of tablets and it runs Intel hardware. But the Pro 2 was a bit too heavy to use comfortably while laying down in bed. I know, I know. It's a first world problem but I don't care.
Either way, don't feel pressured into getting a Samsung tablet just because you have an S5. You can easily have just as good of an experience with a tablet from LG, Google, or a tablet running Windows. Actually, if WinBook had come out with their tablet when I wan on the market, I probably would have gone with that.