Influence of number of indexes on a table

You could have a look into your releasenotes, maybe there is something concerning that. At least in my environment i could not find any limitations concerning the number of indexes. Only the indexsize and number of columns is limited.

Concerning performance: why don't you setup a testszenario and measure the difference?

It is obvious, that a properly constructed index will speed up your query significantly. An additional index has to be managed by the databasesystem and thus creates a certain update-workload when writes are done into that table. You have to find out and decide, if you can notice any major speedimpact in writeoperations.

YOu could also analyse the existing indexes and find out, if there is a way to optimize them. Indexes are evaluated from left to right, so sometimes it is possible to merge indexes, because they both contain certain columns, without having any impact on readoperations.