Deciding Variables with Teres

I have decided to purchase a Teres, but am undecided about some of the variables. I have decided on getting a hardwood base, but am undecided on platter and arm. I currently have a Rega Planar 3 with fairly new Dynavector 20XL. The Teres is much more than I was going to spend (was going to get a Scout), but I would like to get something that I will keep for a long time. Still, I am wondering if getting the 245 is a big drop from the 255 (I believe the difference is lead in the platter.) If the difference is not extreme, I think I would get it to save money and then upgrade in the future, if I feel the need. At that point I might even go for the 265. Also, I wonder if I can start cheap with the tonearm. I could use the RB300 and upgrade later, or I could sell it (I have a friend who would buy the turntable and arm for $300 or so) and buy the Expressimo RB-250 ($480 with the TT) or an Origin Live (maybe the OL1, maybe the Silver.) Would a unipivot make as much of a difference as many claim? Is the difference in platters great? Will any of these tonearm / cartridge combos work better than others? Any comments would be appreciated.

Also, I am concerned about setting up the tonearm, as I have never done it. I found that when I had the Dynavector installed, they did a few things that really helped the sound; in particular, repositioned the setting so that a force listed as 0 was really -1, so that to set 2 grams I put it on 1. I would not know how to do that kind of thing. Would I need a gage? If I change arms in the future, will I have to get armboards or have anything redrilled?

Anyway, just looking for a little advice. I have read much of the archive on this, but find that since I can't hear the TT, my appetite for opinions from many who are so much more knowledgeable than myself is great.