I know that shop and I'm pretty sure they do C41 as well. Maybe they do not do it themselves but ship it to a bigger lab...
Why don't you just ask them? I always found them nice to deal with.
Best to use ambient/natural light (shouldnt be a problem at this time of the year, avoid fluorescent light!), and as you live in Germany, send the stuff off to FARBGLANZ, their scans are really good and
will give you the beautiful skin tones that Portra stands for. Prices are reasonable. While resolution is limited to about 1600px on the long side, for bigger prints you can always have single frames re-scanned by a professional lab later with the Farbglanz scans as "color reference".
If you look at the "Contact" page on that site, "Yvonne Rusch" is identified as being responsible for "Photo minilab production" (as translated to English) and she is clearly holding a strip of 35mm negative (C-41) film.
I have two umbrellas standing right and left with some offset. One with Metz CL-45 that has 7.2v RC power pack and other with 430EX II. Sufficient light, I was quite tempted after seeing photos of Portra 160 in flickr otherwise my choice is CHS 100(120) + APX 100(135) + Rodinal.
I will check out with other studios here in Bremen...