I found a Milchig spoon with the clean Fleishig cutlery. Is it a problem? Also, are there any issues with the Fleishig sponge and by default all the rest of my Fleishig cutlery?

Your Milchig spoon as well as your Fleishig cutlery is all fine. The sponge is fine too.

 

Sources:

רמ״א יו״ד צה, ג: וְאִם נִמְצָא קְעָרָה חוֹלֶבֶת בֵּין כְּלֵי בָּשָׂר, לֹא חַיְישִׁינָן שֶׁמָּא הוּדְחוּ בְּיַחַד בַּדֶּרֶךְ  שֶׁנֶּאֱסָרִים . הַגָּהוֹת ש”ד