The make-up of “an orchestra” in Western art music has varied fantastically over the centuries, and, within any one time period, the number and type of instruments will vary depending on the “acceptable” complement for a particular genre performed in whichever style is wanted (e.g., a Mozart symphony played by a modern symphonic orchestra at full staff, or by implementations of Mozart’s “original” intent–acceptable to him, depending on his mood and financial state, at some time, in some city, or acceptable to, I don’t know, Mendellsohn and an orchestra of his audience expectations) or any other decision by the performers.
And acceptable to the financial resources of said orchestra. Wiki String Section.
Given that, from that Wiki entry: on your run-of-the-mill big-city orchestra, we may find:
The size of a string section may be expressed with a formula of the type (for example) 10-10-8-10-6, designating the number of first violins, second violins, violas, cellos, and basses. The numbers can vary widely: Wagner in Die Walküre specifies 16-16-12-12-8; the band orchestra in Darius Milhaud’s La création du monde is 1-1-0-1-1. In general, music from the Baroque music era (ca. 1600-1750) and the Classical music period (ca. 1720-1800) used (and is often played in the modern era with) smaller string sections. During the Romantic music era (ca. 1800-1910), string sections were significantly enlarged to produce a louder, fuller string sound that could match the loudness of the large brass instrument sections used in orchestral music from this period. During the contemporary music era, some composers requested smaller string sections. In some regional orchestras, amateur orchestras and youth orchestras, the string sections may be relatively small, due to the challenges of finding enough string players.
The music for a string section is not necessarily written in five parts; besides the variants discussed below, in classical orchestras the ‘quintet’ is often called a ‘quartet’, with basses and cellos playing together.
Double-bass section[edit]
The role of the double-bass section evolved considerably during the 19th century. In orchestral works from the baroque and classical era, the bass and cello typically play from the same part, labelled “Bassi”.[5] Since the double bass is a transposing instrument, if a double bassist and a cellist read the same part, the double bass player will be doubling the cello part an octave lower. While passages for cellos alone (marked “senza bassi”) are common in Mozart and Haydn, independent parts for both instruments become frequent in Beethoven and Rossini and common in later works of Verdi and Wagner.
It is a fun game to find the most colossal orchestrations and budget-busters possible…
Not sure what you mean by “titled players.”
Seating arrangements is a whole other thread.