[RPG] Would webs catch fire if Fire Bolt is used on a creature inside of them

The webs are flammable. Any 5-foot cube of webs exposed to fire burns away in 1 round, dealing 2d4 fire damage to any creature that starts its turn in the fire.

As I read this: "Any" indicates that individual cubes can be affected (rather than the whole web). However "the fire" indicates that there is still just one web-fire each round, and a creature is either in it, or is not (i.e. a binary condition). This is consistent with other D&D paradigms in that larger sized creatures do not take more damage from area or environmental effects.

fwiw: (since the 5e writers purposefully used earlier editions for inspiration), the 3.5e text for web said "Any fire can set the webs alight and burn away 5 square feet in 1 round. All creatures within flaming webs take 2d4 points of fire damage from the flames.". It seems like the intent here too was to have individual sections be burnable, but not to have variable (size dependent) damage.

Now I personally might still allow a PC to stretch out the damage by say, burning just one cube each round (which might seem counter-intuitive to the above ruling, but is as least balanced and consistent with other D&D paradigms).

As a general rule...spells do exactly what they say they do, and no more.

In regards to ranged attacks, anything on the other side (or inside) of a Web Spell will be Lightly Obscured.

Lightly Obscured (PHB 183)

In a lightly obscured area, such as dim light, patchy fog, or moderate foliage, creatures have disadvantage on Wisdom (Perception) checks that rely on sight.

This has no impact on ranged attacks.

If the Web could block a ranged attack, the spell would either specify that it grants Cover (PHB 196), or that it Heavily Obscures the area (PHB 183).

Because it does not specify that it creates any of these effects, Web has no impact on ranged attack rolls.