As a beginner, I would look at it from a feature, requirement and budget perspective. It's nice to have all the bells and whistles, but from a practical learning standpoint, I think I use about five percent of the features my Flychord DP420k offers.
These are the features I find either useful or enjoyable.
Weighted keys. This is an absolute must, if you ever hope to develop a solid foundation of good technique.
88 keys. Not essential, but there is nothing more frustrating than trying to play a piece, only to find out there are not enough keys to play it.
Headphones. Practicing requires a lot of repetition. You can easily drive your housemates to the point of them buying a gun to silence you. Headphones provide a good solution to not disturbing anyone. Great for practicing at 4 in the morning, if you're unable to sleep.
Speakers. Play lots of digitals and try to get the best speakers you can afford. You may eventually develop a great technique one day and be able to play with great musicality, but without good sound and tone, your efforts will be in vain. Let your ears be your guide on this one.
Metronome. Built in metronomes are a plus, but not required. If the one you select doesn't offer one, an 'external' one can be purchased inexpensively.
Recording capabilities. Being able to improve requires that you be able to hear yourself objectively. While playing, it is sometimes difficult to do this. Those models that enable you to push a button and record your performance are really useful as a learning tool. Some models will let you play back and increase the tempo and change the key all with button controls. This is useful when playing slowly (how most people learn), but you really want to hear what it will sound like when played at tempo (but are unable to do so, at that stage in the learning process).
MIDI. The instrument can output the real-time playback information via MIDI messages and control external MIDI devices. The instrument can also accept incoming MIDI messages and generate sound accordingly.
USB port. Which can be connected to a PC as an MIDI input or MIDI output.
What I've listed above are the basic features that are important to me. Now, what you need to do is to make a list of your own. Go to as many piano stores as you are able to find with your list, play as many as you can, take notes about the feel, the sound, and anything else you can think of. Compare the models side by side. Then make your decision. It's an important decision. You'll be using it everyday. If you're serious about your piano studies, buy the best you can afford. Best of luck to you.
On the first place, as piano beginner, the tension is caused because you are using dual muscular pulls. Your muscles are interconnected with each other, so if you use two different muscles, you’ll have to balance them.