Customising wireless router firmware

We would like a candidate who can customise firmware for a TP-Link MR-3420 router. The firmware to be customised will be Open-Wrt which is open source. The firmware must have a web based GUI which can be configured by the user. It should be able to connect to a 3G network via a USB dongle and via the standard RJ45 WAN port and must have chillispot installed to allow it to work with our cloud based hot-spot billing software. It needs to have configurable firewall rules, port forwarding and all the basic functionality provided by the routers standard firmware. Also if possible we would like 2 USB 3G modems to be load balanced using a simple algorithm such as round robin. If done well there is scope for a long term working relationship with the ideal candidate. Further details can be provided via personal message.