I want to present my paper to a conference which is related to graph and combinatorics. The problem is I don't understand the quality/reputation of the conference.

The conference has a section "Call for Papers". The conference will be done online. It claims that the selected papers will be published in conference proceedings with a ISBN number. The journal charges a very nominal fee and the invited speakers are from prestigious institions.

I am confused whether I should send my paper to the conference or not. I am worried if the conference is genuine or not. In case of journals there are many checks which can be done on the quality of a journal such as whether it is SCIE or indexed in Scopus and many others.

Are there any checks that can be carried out in case of conferences?

I am worried because since I am submitting my unpublished work, so if the conference is not reputable, my work will go in vain. Can someone please suggest some ways on how to check reputation of a conference?

Another question is If I submit my work to a conference, can I extend the results of that work and submit it to another journal later ? Or is it considered plagiarism?

NOTE: My question is not a duplicate of How to identify predatory publishers/journals since in my question I have asked about conferences and not journals. Finding fake journals is easy as there are many ways to check it but I am asking for some possible ways to check conferences.