New member - old car !

hi there. I joined the ranks of Micra owners last week with my 'new' 2005 car

I bought it for £500 to tide us over for a few months. My wife had a Motability car until her PIP was reduced and we are appealing that decision.
It's a fair car for the price. But of course niggles have emerged. I had to change 2 tyres today and then the engine warning light came on. managed to get a free engine test from Kwikfit - it was the oxygen sensor(s). So my cunning plan is to ignore it.

I also had a free status check from National Tyres when said the N/S track rod end has play. How concerned should I be about this?