Help for newbie trainee hairdresser please

I am a trainee hairdresser and some of my friends have kindly allowed me to practise on their hair. So anyway next weekend I'm doing my friends highlights. She usually gets a half head and I did her colour before Christmas. Her base is 5 light brown and last time I did her colour I used the weaving technique & used the following:

7.8 & 20vol x 2 foils
PL & 30vol x 1 foil
9.73 & 30vol x 2 foils

She loved the finished job but is looking to go a little lighter for summer. She said she doesn't want any reddish tones as she hates that when it's meant to be blonde.

I was thinking of using the following:
Koleston 8.7 & 20vol x 1 foil
Koleston 10 & 30 vol x 1 foil
PL & 30vol           x 1 foil

A friend of mine did mention maybe using 20vol with the PL due to processing time...not sure as I only ever used 30vol with PL.

I was going to start by doing fine slices and then only weaving as I get to the crown - Do you think this colour choice is too light? Is it ok to use the slicing technique in this way? I'm a little bit nervous when it comes to colour - I just need to build my confidence...Any pointers would be very much appreciated.