handling wise
ARBsIMO the best mod that i did last time out of the coilovers, ARBs and WALK. Two chains of thought.
Upgrading both front and rear- this will keep the balance of the car very neutral whilst massively reducing body roll, and understeer. previosuly i had eibachs front and rear on mine and found it excellent although a little to neutral.
upgrading the rear bar only- this will change the balance of the car much more than doing both bars. it will potentiallly reduce understeer more overall, but induce oversteer more than doing both bars would. this time im doing te rear bar on its own, and will upgrade the front if i feel its more oversteering than i expect.
WALKa good mod that will reduce understeer, and increase grip on bumpy surfaces and cornering. it works by increasing castor on the front, giving a heavier, self centring steering wheel, which is nice.
Alternative to WALKIs the superpro castor control arm bush. the whiteline is a similar bush in a shiny mount, this is the same sort of bush that will go in your existing mount, for the same results at less cost.
http://www.jbsautodesigns.co.uk/product/2982/front-control-arm-inner-rear-bush-kit-with-caster-increase-and-anti-liftcoilovers/suspensionto be honest do you really need coilovers is a qquestion you need to as yourself, because a good set of springs and dampers might be exactly what you need.
Brakesthese porsche brakes look ace, and im very likely going to get myself a set after summer, hoever in the mean time im uprating my pads, hoses and fluid, which should give a very large improvement over stock.
And its either the boxster brakes or handling mods like coils walk and arbs
id say uprate your pads, hoses and fluid for the minute and see how you get on with them, and i the ARBs to your car. that way you will have greatly improved the two biggest weakpoints on the mk5. Body roll and brakes