If you don't positively know differently, it is always prudent to assume that ANY wall is a load bearing wall. By "Vertical beams" I assume you mean "studs" or maybe even "post" because "beams" are horizontal structural members.
How do you know you are dealing with "4x4's" unless you already dug into the wall? If the wall is approximately 4.5" thick then it is probably just a 2x4 wall, not 4x4 which is a structural member, or post. If you do have a 4x4 (or 2 or more studs all nailed together) in the wall it is almost definitely load bearing because why else would someone use it instead of just one stud.
I don't know that enough could ever be learned in books (or in Internet message boards) to qualify you, or anyone else to be able to know how best to proceed with this job. It is easy if you know what you are doing (what isn't?). Anyone that presumed to be able to tell you exactly how to proceed would be irresponsible because it is likely that you could damage your condo or hurt yourself because you don't have the experience to know what can be done and how.
With that proviso in mind, here are some general ideas (below). I am not proposing that you attempt this job yourself because in my opinion, the questions you asked told me that it would be best if you left this up to someone with more experience. - Generally, bearing walls have another wall or beam or girder and posts lined up directly below them in the basement (if you have one). - It is common for the wall to fall approximately in the middle of the house and be perpendicular to the floor joists. (Do not attempt this job if you don't know which direction the floor joists run.) - In most cases, to create a simple door or passageway in a bearing wall, it is possible to install a structural header over the opening. First the joists above need to be supported and braced; then a couple studs removed and the header, cripples, and jack studs cut and installed. - Be sure to locate all electrical wiring, plumbing and possibly wall cavity air return wall bays and know how they will impact your plan. - There are other considerations as well that only experience can account for.
If you don't know what you are doing and you mess up you can decrease the value of your condo or even hurt yourself. You at least need the "on-site" advise and guidance of a professional.