How many files in a folder is too many?
You can easily try this yourself by running the following in Terminal

mkdir ~/t
cd ~/t
dd if=/dev/random of=test bs=1024 count=16
for i in {1..10000}; do cp test test.$i; done


to create a folder containing 10'000 files with 16kB each (replace the 16 in the third line with another number for differently sized files).