NewMuslims.com has sections entitled Marriage Advice parts 1 and 2. Importantly, it's ill-advised to rush into marriage.
For a new Muslim, this author would advise to wait at least a year, preferably more, before thinking about getting married. Marriage is a big decision and one must allow oneself sufficient time to grow before making such a life-changing decision.
It's particularly dangerous for converts: they rush into marriage, wind up getting divorced, then leave Islam.
NewMuslims.com has a page The Nuts & Bolts of an Islamic Marriage. Relevant here is:
In Islam, the marriage is a contract between the two parties. The four
basic conditions for the marriage contract to be valid are:
Consent of the woman’s walee (marriage guardian)
Agreement of the woman
Two male, Muslim witnesses
The offer to marry and it’s acceptance
There are exceptions to the consent of the wali (e.g., if she's been married before, and depending on which fiqh is involved); see If a girl marries her boyfriend without her parents' consent, is their marriage accepted by Allah?
However, one should not take the wali's lack of consent lightly: they will still exist even if you get married, and it's unpleasant for a woman to be torn between her family and husband. This will likely put a strain on your marriage.
Also would I then become her main guardian?
Basically, yes; see What role does the wali (guardian) play after a woman is married?
Or should we wait till my divorce is completed?
Yes, it's just common sense. It gets messy if you're married to one woman Islamically and another woman legally. And it would be unpleasant for you're prospective wife to be dragged into this mess.