If I had a project or two under my belt or had the time to line up a group of investors, this is what I would propose.
Adaptive reuse of both the Barnes Bank Building and the SL Roasting Company building. Directly adjacent to the SL Roasting company building on the west side I would step up to 4 stories, half way to the corner, then from that point I would step it up to 8 or 10 stories for the rest. The 8 or 10 stories would be adjacent to the Barnes Bank Building, (already at 5). The four story section would wrap around the back of the SL Roasting Co building, and on the east side I would either step it down to 3 stories and 2 stories. Giving the frontage on 400 S some variety. All the upper floors would be residential.
I would push for the parcel east of Blair St to be 6 to 8 stories, with a mix of office retail and residential, instead of the proposed 3 stories.
For the parcel south on Blair St I would push for 6 to 7 stories instead of the suggested 4.
The reason I have the mix of 3 and four story front west of Blair is to better mix in the existing 2 story SL Roast Co building. The reason I feel there needs to be much more density there is that the entire purpose of the Transit Station Center zoning is to maximize the density around certain Trax stations, and it needs to be maximized. There is also so much open space on the Library and City Hall blocks that more people living in the area will provide more usage of those highly underutilized open spaces.
Yellow - 3 stories
Orange - 4 stories
Blue - 5-7 stories
Purple - 6-8 stories
Green - 8-10 stories
Bright Green I wouldn't build on to allow for the potential of a future mid-block connection, whenever 400 East gets redeveloped.