I am an adult piano learner who is completing level 2. Looking for buying a digital piano to help in my further learning. . . . What is the best piano for my price range that helps in leaning advanced levels as well? . . .
You may want to upgrade to another DP (at a higher price, unfortunately) as your playing progresses.
Unlike acoustic pianos, DP's don't tend to be "lifetime purchases". They are relatively cheap, their technology changes fairly quickly, and the cost of electronics continues to fall.
Right now, you can get a $2000 DP (say, a Roland FP-80 as an example) which is better than those on your list. That piano will probably be replaced in the Roland lineup, in 3 years, by something better, at a similar price.
And you might decide to buy its replacement, then.
PS -- bias -- I own a PX-350, and play it through Pianoteq software. The PX-350 alone is certainly adequate for what you want to do _now_. The PX-350 plus Pianoteq improves the piano sound, but doesn't change the action.
PPS -- the Roland RP401R is an interesting DP. It uses the "PHA-4 Standard" action. Unfortunately, that action isn't on the "recommended list" of the only conservatory that has popped up as accepting DP's for its exams. There's a long thread about this question, here:http://www.pianoworld.com/forum/ubbthreads.php/topics/2317687/1.html