So here's the thing... had I not given you the 'cute' response, I would have actually just pointed you to the OpenVPN on OpenWrt guide that is the first hit in the search because you asked for a step-by-step guide.
From the sound of it, that wouldn't have helped since you're saying it is a bit overwhelming (and I do get that -- sometimes you want a basic overview first rather than all the details). Asking specific questions will result in specific answers -- I'm not saying that to be snarky, but serious -- if you are confused about a specific aspect or you need more information about one implementation technique over another, please make that more clear so we can point you in the right direction.
It sounds like you are genuinely interested in learning about this stuff, but I seriously would start by reading the link that @jeff provided about VPNs and look at this entry about Tor to figure out what you really need.
The best and most authoritative documentation of how to configure and use OpenVPN is in the "community" section of the OpenVPN site. On OpenWrt I still recommend using a native style .ovpn config file for your client or server rather than the UCI system.
disclaimer I have not read all the posts above, but I use Torguard. Torguard is inexpensive per month, they guarantee to keep Zero (0) logs, and have no issues connecting my router to them; hence tunneling all of my LAN traffic past my ISP and internet to the Torguard VPN server. In other words my router is the VPN Client and Torguard is the VPN server. There are clear instructions and configurations you can just copy, and be up and running fairly quickly.
Speed is going to vary, but I get about 80mbps down and 120mbps up with my current configuration. With the Linksys 3200acm I am not CPU bound at those speeds as they average around 40-60% at peak flow. Your CPU% will vary depending on the hardware available.
I think that it depends on your particular needs.I always use VeePN service in order to get the access to content that I need, such as websites, games, streaming media, streaming music or Netflix. And it really helps in such situations a lot. Additionally, vpn services can be very useful in order to increase online security and privacy level, in this case I am not sure that such decision will perfectly match your situation.