The 9-18 is only average in IQ and is not that small, but price is ok.
If you're only going to get one lens for both indoor portaits and landscapes I agree the panasonic 20mm is the best compromise. The Olympus 17mm f1.8 is an option if you want a bit better build, and it's gorgeous on the silver e-pl5.
The Panasonic 14mm f2.5 is a tiny landscape lens with good IQ, it can be had for about $175 on ebay.
The Olympus 45mm 1.8 is a fantastic portait lens which is great bang for buck.
Just got the e-pl5 and I'm loving it with the cap lens