I have a section comparing digitals, uprights, and grands, in link below; see section III.17. Digitals are starting to make uprights obsolete, although a few die-hard adherents still insist that the only pianos are acoustics, but the numbers of those die-hards are decreasing every year. Your digital will serve you well until you decide that you need a grand, and you will KNOW it when that happens, so don't worry about that now. However, note that pianissimo is difficult on a digital, and the dynamic range is inferior to most acoustics. Therefore, play on acoustics as often as you can, tho that is not a necessity. When playing on acoustics for the first time, you might find it quite difficult. This is normal and happens to everyone, not because they are better; they are just different and you just have to get used to it. Sometimes, in a few minutes, or at most a few hours, you will get used to it and it will play just like your digital, whether you try an upright or grand. Most grands will be easier, especially once you get used to them. The average upright out there (some are REALLY old) will feel difficult to play and some will be unplayable, and most would be out of tune. And you would be right. The only time you can guarantee an upright that might be superior to your digital is if you got a brand new one of good quality, well prepped. Finding good, used uprights is a very difficult job. After you've had the upright for many years, you will have a hard time selling it.
I have a Steinway grand and a digital -- I need both, and use the digital frequently.