Heh, yeah, Hangul looks like it uses ideograms like Chinese / Kanji, but it's really an alphabet!! They just put words together in a more compact form - unlike us stupid westerners who use one space per character with Latin alphabet; such a waste of space!
Language proficiency, level of being bilingual / multilingual, interference between languages, etc., is nothing clear cut and simply depends on how much each person has done , what their circumstances were, etc.
I started out bilingual. I was born and raised here in the United States, but my parents are from Central America, so I learned both English and Spanish together, growing up, at the same time. Still, english is language No. 1, and Spanish is like my 1.5 because I'm simply more exposed to english, despite always talking spanish in the house. My classic example is, I don't know what the word for "anvil" is in spanish. I knew it in english from cartoons, TV shows showing metal-working, orchestral, but when would "anvil" come up in family conversations? like never! I've looked it up like 4 times and I keep forgetting though.
my mother also always exposed me to French with french kids shows off educational channels, french cartoons, etc., so it was the natural choice for my third language. The exposure over the years means i'm very familiar with how French sounds so I'm usually one of the best in class when it comes to pronunciation - when I mess it's because i'm having a hard time keeping the good pronunciation while trying to keep the sentence flowing smoothly. However, the more advanced conjugations still throw me off, and my vocab is limited, so although I can read French and understand it pretty well, i'm not fluent, and I need some time listening before I can understand the spoken language better.
The only confusion I've had between the languages is wen a word is similar in all three languages, but French has a subtle difference. ie, the word Practice. In Spanish: Practica. In French: Pratique. THERE'S NO "C" BEFORE THE LETTER "T"!!
For my 4th language, I wanted to go to a different family, so I didn't want Germanic or Romance languages anymore. I was considering Hindi or other Indian language, or Japanese, because I wanted a new writing system. I wasn't going to start soon though; I wanted to become more fluent in french first.
But then I found Japanesepod101. Add that to my watching subbed anime, and I couldn't pass this up, so I guess i'm learning Japanese now.
I could point out though, although for some reason I can't think of the exact circumstances right now, there are certain situations or kind of days I have that gets me feeling weird and my mind goes into scrambled multilanguage mode.... I start thinking things in english, spanish, french, japanese, and any other random words and phrases i know of other languages. I THINK it's when i've been working too much on the writing system for language i'm making up myself for my scifi (which is, one of the other motivations for learning more languages.)