As a Shia convert, is talking to Sufis considered breaking the third Shahadah? Will it lead to apostasy from Shia Islam? Can I still identify as Shia if I had contacts with Sufi orders?
You do not become an apostate or break the third shahadah by speaking with someone who has a different belief or by being present at their gatherings, unless you have the intention of apostasy. (This is true whether they are Sufi, Christian, atheist, or any other group.)
However, sometimes, when we are solidifying our religious identity, especially after a recent conversion, it is helpful to stay within the confines of our religious group and avoid contact with others. But this is a psychological or spiritual matter, not anything relating to apostasy.
You are a Shi'i if you wholeheartedly accept the authority and spiritual status of Imam Ali (a), without any competitors, and identify as Shi'i.
If you had any belief which is incompatible with Shi'ism, you may reject that belief and remain Shi'i. Similarly, if you gave bay'ah to someone other than Imam al-Mahdi (A) (for Twelver Shi'a), you can declare your ultimate bay'ah to Imam al-Mahdi (A). If you acknowledged the authority or lineage of someone (living or deceased) who is incompatible with your allegiance to Imam 'Ali (A) and Imam al-Mahdi (A), you may choose to reject that authority.
Sufis differ from one another, and some are closer to Shi'ism than others.