Numerals and nouns combine in weird ways in Russian. In the nominative it look as follows:
- 1 мост
- 2 моста, 3 моста, 4 моста
- 5, 6, 7, 13 or 1000 мостов
The form depends on the last word of the numeral (e.g., 21 is двадцать один, so you use the singular form)
This is a consequence of Russian having the dual number in the past. 2 used the dual form, whearas 3 and 4 used the plural. Bigger numbers were treated like nouns (e.g., "a bunch of bridges").
As the dual number decayed (in most Slavic languages, really), the missing forms were hastily replaced with the Genitive singular; then 3 and 4 aligned with 2. Why? For no good reason; Polish did it the other way round (in Polish 2,3,4 all take plural nouns). The result is a mess you see now.
“In town” should definitely be accepted. Can be in one of several towns or of a particular one if only one is likely/possible. “In the town” Refers to a particular town. “In the city” means one particular or one of several cities. “In city” is not used. I am a native English speaker, but not a linguist.