1. You can always sell the switch or if you are like me then you will keep it and use it for some of your experiments. What is the interface speed of your switch, 100 mbps or 1gbps?
If it is 1 gbps then keep it to share files over LAN otherwise sell it.
If you want to buy just a router then go for TP-Link or anything but if you wanna buy a Modem/Router then IMHO you should choose ASUS.
2. If you just wanna use internet on mobile through wi-fi then why not use your LapTop's wi-fi adapter as hotspot? So easy to do in Win 7, even some apps can do this for you. Provided that you do have a wi-fi capable laptop.
This would be the cheapest option.