A parameter to limit the amount of feed items used

Well, for this you'll need to write your own process function (based on processXML or similar). Please check README.txt to see how to create your process function.

Checking in each loop if limit is reached will slow down import and we don't want that.
If you need help with process function just write it here.

I completly forgot about xpath's position() function! You can use this to limit your results, just add it in "Enter parent item xpath" field.
Let's say our parent xpath is

//vehicles/cars

and to get only first 10 cars we can use

//vehicle/cars[position() <= 10]

Note: this don't work for processXMLChunked and processXmlReader functions!