- 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.
- DonIf you are in doubt, don't use ~でございます, and 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. But having one or two ございます wouldn't hurt if your Japanese is fluent enough.
- An expression of 自発 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 ~"). Even when you want to express your own opinion, ~であると考えます ("I believe/think ~") is enough in an academic context. There are humble versions of 思います/考えます (推察いたします, 存じます, 愚行愚考します, etc.), but these are mainly for respectful business letters, not academic talks.