How do I know if my startup name is too broad to get a trademark for it ?

I'm not sure what you mean by the name of your company is "too broad," i.e. if you are referring to the name describing an aspect of the goods or services (in which case we say the mark lacks distinctiveness or is descriptive); if the goods/services are very broad and encompass many different commercial fields; if the mark is to be used around the world and requires registration in multiple countries; or if you are aware of one or more other businesses with a similar name; or some other issue? However, as Mr. Mincov has suggested, a good place to start is to consult a trademark attorney in your home country and have a trademark clearance search conducted. The trademark clearance search can reveal a number of useful items of information including but not limited to 1) if a similar business exists with a similar mark such that there is a risk of liability for trademark infringement or the mark will not register over that third party mark (if also registered); 2) if the mark lacks distinctiveness and may not be that protectible; or 3) if the mark may be difficult to register for some other reason.
I can provide you with additional information and handouts if you want to contact me directly.