Hello!
I did a service on a Smart 2006 two seater, I had to drop the sump to remove the 0W 30 oil (As NO Drain plug) the filter is a paper one located behind the big black plastic cap on the engine with a huge nut shape on the top.
I have since purchased a oil suction pump to pull the oil out through the dip stick hole, I enquired at Smart and they said Sumps were in the process of having drain plugs fitted but I havn't seen one yet. Maybe you are a lucky one?
Oh! as for grade, it really depends on climate and conditions, your Spares supplier/stockist will have the Bible on all recommended lubricants for all makes so He/She will advise you the correct grade.
Hope this Helps!
Press the Blue Button please to appraise my FREE! Effort.
Thank You & Good Luck!
Paul 'W' U.K.