Dear Ariadna

thanks a lot for your message.

High pass filter is ok, the important thing is to do low pass too, and no problem if you do it twice.

About spatial smoothing, you can include it (it's better to extract nuisance variables white matter/CSF from unsmoothed data) or not include it if you want better spatial resolution.

If you download the rsHRF plugin for SPM, you will find the suitable preprocessing options for example in this demo job

./spm/rsHRF/demo_jobs/vox_deconv_job1.mat

Hope this helps.

Daniele