Your jack plane is going to be your #5. #6 would be a fore plane (I don't think they're that popular, I don't see much mention of them here), and 7's and 8's are jointer planes. The #1,2,3,4 are smoothers, 1 being the shortest, 4 being the longest. I don't own anything shorter than a #4, and find it sufficient for what I do. Some people, including myself, also have another #4 set up as a roughing plane, with an aggressive bite for quickly taking down high spots before using the jack and/or jointer. I just finished flattening a 24"x72" table top glue-up…the glue up was decent so I went for the #5 at a diagonal to flatten front-to-back, then at the opposite diagonal, then the jointer lengthwise, followed by the smoother. I gave it a quick sanding (took much surface area for a card scraper IMO).
A card scraper is a thin piece of metal that gets a tiny hook (think, so small, you can barely catch a fingernail on it) that you use to scrape the surface. It will produce a finish-ready surface, and can save a lot of sandpaper.
Google will be your friend here, do some searches on card scrapers.