- In my opinion, 留学いたしました and 留学しました are both okay in a self-introduction. The former may be preferred in some companies, but from my experience, a boss in a research facility tends not to expect you to use stiff humble language like this. YMMV.
- Don't use ～でございます, stick to ～です. ございます is still used at some classy hotels and restaurants (as well as fantasy manga and such), but it is usually an overkill in a job interview.
- An expression of [自発][1] like 考えられます/思われます does not have a humble version. It's already indirect enough because the existence of the "thinker" is obscure in this form. To introduce an already accepted idea in your field, you can safely say ～であると考えられます ("It is believed that ～").


  [1]: https://japanese.stackexchange.com/q/42680/5010