Good News Translation is correct in beginning a new paragraph at verse 18. This paragraph is not related to verse 17 any more than verses 14-16.

And the standard of the camp of Reuben set out by their companies …: The instructions concerning the camp of Reuben in 2.10-16 (see the comments there) are carried out in verses 18-20. For the standard of the camp … set out by their companies, see verse 14. The camp of Reuben included the tribes of Reuben, Simeon and Gad, which camped on the south side of the Tabernacle (2.10). Since the verb set out refers to repetitive action, Good News Translation says “would start out.” According to 2.16, they were to set out “second.” Although this idea is not repeated here, Good News Translation makes it explicit at the beginning of this paragraph with the word “Next.” In many languages such a word will make the translation more natural as well as clear.

And over their host was Elizur the son of Shedeur: See 1.5 and 2.10. For host see verse 14.

And over the host of the tribe of the men of Simeon was Shelumi-el the son of Zurishaddai: See 1.6 and 2.12.

And over the host of the tribe of the men of Gad was Eliasaph the son of Deuel: See 1.14 and 2.14.

Quoted with permission from de Regt, Lénart J. and Wendland, Ernst R. A Handbook on Numbers. (UBS Helps for Translators). Miami: UBS, 2016. For this and other handbooks for translators see here .