Learning two languages simultaneously would be a help or a hindrance?

[Jan]

Probably ,it depends on languages which you are going to choose.
At the same time,it differs between nationalities
, your mother tongue shall give you better grasp on some of languages ,while other would be simultanleously much more complicated.
It is said that for Polish is not recommended to learn English and German but supposedly, it is good ,or at least no problem, when Polish native speakers would begin to study English and French together.

That plan which you have depicted above, looks very impressive.

I wish you a lot of fun while studing .

Myself, I would take a risk ,at least the risk to start, you could evaluate quite soon your progress and would be able to decide, if is better to limit yourself just to one of them or both are no problem.
I think after one year, it would be possible to see if that has some sense,though somebody could have had some bad experience about studing together French and Italian, it does not need to work same way in your case, many people are very gifted on a linguistc field.
Jan