Brian -
Yes, the 2.8 versions are heavier. Not by a huge amount, but noticable. No difference in 3.5 vs. 2.8 provided they are both Planar or Xenotar models. Many of the Rolleiflexes were made with 3.5 Tessars, however - those are different.
I have owned Rolleiflex (many models), Autocords, and 2 Yashica-Mats. They all focus no closer than 3 feet. Even if they did, you would be having serious parallax problems at that point. Using the close up lens sets correct the parallax and allow you to focus very closely. They are not a pain to carry - they are the size of a filter and attach the same way.
BTW - after all the TLR's I have owned, the only one I kept was my Ricohmatic 225. A nice camera similar to an Autocord.