Sorry I didn't see this before.
The SVT Focus is not a typical Timing belt job. Many of people have had an issue doing it wrong and there are also many who have done a good job at it. Myself and SleepyBoy on here have done ours several times (mine because I bent a few valves a couple of times ... it happens).
These cars are interference engines and if the T-Belt is wrong, it can be very very catastrophic.
For the T-Belt you will need the Timing Tool (Both CFM and Massive speed sell them) about a 35 dollar part and it comes with a bar to hold your cams and a pin to let you know when you are in TDC.
The rest is a long story, and there are many on here for that info.
As for the P0420, yup, need to change our your O2 sensor ... does the car have a cat? If not, you may be on the stock tune and it's just reading bad because of no cat ... if you do, then they are probably just busted. Easy fix.
P1381 - Back to the Timing belt. Since the SVTF has a VCT, that makes the timing very tricky. Again just doing the job right and making sure everything falls in place correctly will fix that. It's going to take a couple of tries for those who don't know this. Even experience mechanics that are not familiar with our cars will get it wrong.
P1518 - That would be your IMRC. It's a box that controls a switch to the runners of the Intake Manifold. It either needs to be replaced or fix. There is a How-To on here as well on trying to fix it. You may just luck out on the fix because it is common.
Sorry again that I missed this. But don't worry we are all here to help you through each one. As many many many SVTF Owners have been there and done that. including myself.
Ask away and we will help you as best as we can through the internet.
Hatch Nation Member: #147
R.I.P - FELLOW FF MEMBER, IZZY, BLK2k3GTS, will always be remembered. We will compete on a different course again one day.