Since you are close to the transmitter you probably don't need a signal booster but a distribution amp. Wineguard would work well.http://www.winegard.com/offair/amplifiers.php
You need to place it as close to the antenna as you can and use high quality splitters. If you have RG59 coax RF cable it would be an upgrade to go to RG6 or RG11
Not many choices for HD DTV tuners. You could try this one.http://www.hdtvsupply.com/hdtv-tuner.html?gclid=CL3MtP_b-bMCFcuZ4Aod5HIA0w#axzz2Dp1MDvW9
or a TIVO so you can record programs and time shift.http://www.tivo.com/products/tivo-premiere/index.html
Having to boot a PC and turn on the TV just for Pandora makes it a bit of a pain so I would suggest using an AV receiver with Airplay so you can wirelessly stream it from an iPhone or iTouch, some AV receivers have Pandora, and the best way to access it might be Sonos. Great control, multi-room capability and fantastic control interface. Also plays many other online services, internet radio and all your music files.