It's a custom laptop, would it run with all the default options on the site?

http://www.custompc.ie/gamer-w650sh...0m-133944-p.asp

Maaaaybe. The big three components that you have to get right for TS3 (and TS4) are CPU, RAM and GPU, and on each of those it's an "Okay... probably, but not great". I'd definitely recommend jumping up a generation on the processor and getting an i5, because the Core2Duo is not up to running TS3 with all EPs. You'd do better with a couple gigs more RAM, but you can add that later - and you'd do better with a slightly stronger graphics card, too. If I were you, I'd switch the CPU to the i5-4200M and the graphics card to the 750M. It's another €215, but it's worth it.

For TS4, EA have said the system requirements will be lower than for TS3, but we don't know how much lower yet. So in principle, anything which is good for TS3 should be good for TS4 - assuming you trust EA's word . If you don't need to buy a new computer right away, you might want to wait and see what TS4 ends up needing before making any decisions.

Thanks!
I don't really play any other games other than The Sims, so all I'd be doing on it are everyday things and TS.

To be honest, there are very few games which need more computing power than TS3 does. Lots of games you can turn the settings way up to get great performance, and that requires lots more than TS3 does - but I don't know of another game which needs as much as TS3 does to just run fairly smoothly and not crash too much.