"olyan" is similar to "ilyen". For example: "I don't want an apple like this, I want one like that" means "nem akarok ilyen almát, olyat akarok."
just as gwe1980 said, ilyen = like this, olyan = like that (though i'd like to mention that "like this/that" can also be translated to "így/úgy", which refer to the manner of something (answering "how"). Ex.: do it like this = csináld így. "ilyen/olyan" refer to state what something is like (answering "what .... like, what kind"). Ex.: egy ilyen autó = a car like this Egy ilyen autó az álmom = my dream is a car like this)
English is too simple for that.
This (a demonstrative pronoun) is ez in Hungarian.
This (defining an uncountable amount) is ilyen in Hungarian.
I'd mention "ennyire" too, "Ennyire magas" is also fine and it's plain to see this is related to amount/measure since "Mennyi" is roughly "How much"
Without context this English sentence doesn't make sense. What is the idea behind this sentence? Something like: "Is it that tall, or this tall?"
kinda. 'This - ilyen' here indicates a reference to something you may be pointing at, so 'this tall' refers to that thing's height. Here's an example (yours was good as well though): - How tall is your sister? - Hm, she's like this tall (you say, holding your hand out to show the height)
I hope it helped. If not, feel free to ask :)