Ya, the charts are made for a party of four. Here's what you do. Design a Dungeon Crawl or other adventure that is heavy on the fighting. Have some ecounters CR 6, some 5, some 7, etc and basically play around with them adventuring until you get a good idea of what you need. Personally, numbers help so I think a single opponent of CR+2 (average group level +2) might be about right. Just watch out for high DRs and SRs and ACs that may be a little on the tough side.