Learn English – Is it correct to write “offer of” or “offer on” and “whenever suits you better”

Both sentences mean about the same thing, though I think they're using different senses of focus. In "My main focus is Spanish", the word focus refers to the thing that is being focused on; in "My main focus is on Spanish", the word focus refers to the relationship of the person to the thing that they are focusing on. Using the definitions from the Free Merriam-Webster Dictionary, "My main focus is Spanish" is using sense 5a, "a center of activity, attraction, or attention", whereas "My main focus is on Spanish" is using sense 7, "directed attention".

Either way, the sentence ends up with roughly the same meaning. However, depending on the context and exact meaning, I think one could be preferable to the other. For example, I think "My main focus is Spanish" tends to preclude "My main focus is subject–verb agreement", whereas a person whose field of interest is already known to be subject–verb agreement could well say "My main focus is on Spanish" to indicate that their main focus is on subject–verb agreement in Spanish. But this is a very minor difference.

The problem is that the front-shifted modifier dangles: it is not I but rather the future research that can more properly be termed consistent with the previous experience. Thus a possible correction would be

Consistent with my previous experience, the research that I am interested in pursuing . . .

or

Consistent with my previous experience, my research interests include . . .