As the copyright owner of the source code. You are fully within your rights to license your software as you see fit. Even if this means multi-licensing. When multi-licensing, you offer end users/developers multiple options to license, in which you can either dictate the conditions of which license needs to be used, or simply allow them to choose which license they wish to use.
I want to sell in the future, but for now I want to give it out free
This is no problem, even if you choose to multi license from the start of distribution.
Note though, if you choose to release under an open source license to begin with (e.g. MIT) and then change the license later on, code released up to that point (or if it used by others up to that point) does not change, and can remain under the license it was original released with. This means current users may still meet the conditions of a non-proprietary license and thus can still carry on using it.
There are of course caveats if you were to put conditions in the original license, however this may defeat the purpose of the open-source license you use in the first place (e.g. permissiveness for MIT) in which case it may be better to release under say GPL to prevent others from 'closing' any source they use rather than a permissive MIT/BSD style one.
but still want my company accredited in some type of way
Even for permissive licenses such as MIT and BSD, any conditions you state must be met, and this includes reproduction of the license text (and they usually include disclaimers and accreditation). This ensures that any accreditation would be reproduced by subsequent parties.
Should i make my code proprietary from the start and put my logo on it
or should i make it open-source until i decide to sell it?
Unfortunately this is a question only you can answer. For me personally this usually boils down to...
Do I want others to be able to use what I have done however they see fit with me simply knowing that they know I wrote it. In which case permissive license, but I also fully expect others to be able to capitalise on my hard work without me seeing any monetary benefit.
Or
Do I want to see what everybody else can do with my code, not worry about getting credit (Directly that is. I'm sure if you really wanted to prove you wrote it, source control history would no doubt shed some light on the authors/contributors), but also sleep well knowing that (although there will be people who do benefit financially, by building and distributing it) I could potentially keep track who is monetising it. In which case a copyleft license.
Also note, open-source does not mean you cannot sell it (in fact in the case of GPL, it is actively encouraged). Code may be open-sourced, but this in no way implies that it can be used. It just removes the physical barrier of code visibility.
Open-source is a bit of an umbrella term, and it could be argued that the many open-source licenses available are effectively different interpretations of the definition of 'open-source'. To me, it literally means that source code written by myself or my company, is visible by parties outside of my company. How they are allowed to use this open-sourced code is down to how I choose to license it (if at all).
Furthermore, how do I brand a piece of software if I decide to go
open-source? Should I just put my company name in a comment in source
code? Or should I still put a logo in the GUI? Or is it not possible
to credit the developing company in open-source software?
You could certainly get credit no matter which license used, but branding is something which would probably require you to add clauses to licenses such as BSD or GPL, which state that your logo must be displayed, or any affiliation etc.
Remember, You are the author, you are the copyright holder, you dictate the conditions of any license you wish to release under.
Be aware though, if you add clauses like this to a permissive license, it's no longer permissive. Likewise if you do this to a GPL one, while it probably could still be described as copyleft (IANAL), it certainly would no longer be GPL. So legally speaking, you (or they) wouldn't have the same rights as if you retained the GPL in its original form.
