I have read a few different things with differing statements on the web and am asking here to find out what the truth is before I start my 1st world population.

Are the following things true or false?

1. Imported sims will not have any skills in the actual game unless you do this in CAW? If this is true do you use master controller or something else, this is especially confusing to me after reading too many conflicting views.
2. Imported sims will not have any career/service/role but this can be fixed using master controller.

Also, I can't use edit in game in CAW unless I remove my DCCache folder, which makes my store stuff be not there so the whole missing object substitution is going on. How do I get around this? There's some store CC and so on I'd really like to include in my world.

And is there anything else I should know before I do this my 1st time? I'd appreciate any tips from more experience users.

What do you exactly mean with population and "imported sims"?
I will try to give my suggestions, depending if I understand you right
1) Imported or placed sims from library in Edit town (where you can also save families) - do keep sim informations like skill, favorites, traits, job, job levels as far as I know, if you place a household with more than one sim also the relationship, relations between them.
Sims from SavedSims folder don't have career informations or skills.

2) I think when populating a world with sims from library they "can have" a career saved with them, and when placed the sim will actively join this career.
Service and Role sims get there "job" automatically by the sims3 system (with Storyprogression genetics can be mixed in from bin library sims), are not real town residents.

If you mean CAW - Create a World tool. As far as I know it is not recommended to populate the world file itself, but
create a game play save which you populate with sims. So with the world and your save you have everything.

But here is a tutorial how to http://simswiki.info/wiki.php%3Ftitle%3 ... CAW_Worlds

Yeah, I was talking about CAW not the actual game itself. I'm good as far the game goes, but this will be my 1st time building a populated world though I've wanted to try it for a while but seem to always have a lot of other stuff to do.

The tutorial does seem to answer my second question with the bit "To add Sims to the hidden Service NPC household just click on a Sim and select MasterController's Advanced > Set Service command. Choose which service you want your Sim to perform and when the game loads up the Sim you chose should be your new Mailman or Repairman."

However, as for like say adding a doctor in CAW do I need to set the career to doctor or will my doctor sim in the household bin's career just be imported, will his logic skill still be 10 or do I need to set it to 10? If this is true do you use master controller or something else in CAW? This is the question that is really left unanswered.

See this thread at MTS, I think the how-to step by step for is what you are looking for?
https://modthesims.info/showthread.php? ... ost4073487

As a tipp, when you test your world file (you can also do it with any other world), don't install the common way,
simply paste the world file into the game installation path
C:\Program Files (x86)\Electronic Arts\The Sims 3\GameData\Shared\NonPackaged\Worlds

This way it is easier to "uninstall", because you only have to delete the file and the world caches of this world.
(of course when deleting saves will not work anymore)

Yeah, that answers my questions exactly. Thanks a lot and a major league thanks for the tip, will certainly make my life easier.