Is it religiously sound to decide not to have a religious and well-mannered suitor propose now, but rather to postpone the matter until he is financially ready and a wedding date is set, with the intention of providing financial assistance to expedite the marriage, or is it better to let him propose now, and what is the maximum duration for returning to the homeland to complete the marriage?

It appears that delaying the engagement until the suitor is ready is preferable. You must fear Allah and know that this world is fleeting. If your continued stay in the country of study poses a risk to your religion or your honor, then it is not permissible for you to remain, and you must return to your family. There is no specific limit for your stay outside your country; the matter depends on the extent of your security concerning yourself and your religion.