Already got a Diesel Tuning box, just wondering what other modifications people would recommend on this car.

You can fit stuff like the PD160 intake and an aftermarket panel filter, that's what a lot of the Furby vRS owners do with the 130. You can also run it without a catalytic convertor. TrevorB33 did this with his 110 which was running around 140bhp IIRC:

http://briskoda.net/octavia-i/updating-turbo-mk1-octavia-110bhp/135718/

Koni FSDs, maybe a brake pad upgrade, and decent tyres all round.

Getting much past 140bhp means things like a hybrid turbo and new injectors.