The best advice any one can give you is to locate the ejector basin on an area you do not plan on finishing that part of the basement for future service of the pump. The pumps are very nasty and dirty when you need to replace them. Also do NOT install it in a small tiny ass closet. Make sure there is enough room for a full grown 200+ pound man can get to the pump pit area to work on the said pump.
I had one where they closed of the area under a set of stairs. the cubby had a 2½' x 2½' foot access panel that I had to crawl through, and the space was only 4' x 4' square with a ceiling height of no more than 3½' tall. needless to say working on that pump was no fun. Oh yes forgot to mention the thick snow white shag carpet at the access panel.