As far as toys go, trains aren't usually that big so it should be easy to store.
Also, loaning is a great idea - the Thomas sets are well made and the set that we have has been through 3 other sets of boys and the paint still looks practically new (even on the wood sets!).
My LO loves Thomas and having all the trains and gear has been helpful for his development. He can name all the trains/colors/parts and the coolest thing for us to see is that he can already identify the numbers on the trains, counts to 10 and puts the trains in order up to #4 and he isn't even 2 yet - such a versatile toy really :)
Even if your LO doesn't like Thomas, it such a popular set that you'll be able to find someone to enjoy it.