Car seat positions in Caravan

I have an almost 3.5 year old who is currently in a Cosco Summit booster and still using the 5 pt. harness as he is only 34 lbs. Our Caravan does not have Captain's seats, we have the short bench installed as the 2nd row seat. His seat is currently located behind the passenger seat, except that because the bench is short, he is half behind the passenger seat and half in the middle (does that make sense??). We are expecting our 2nd in the next couple weeks and don't know whether to move our summit seat over to behind the driver and put the baby seat where he was. This seems to be the best option as I'd have access to the baby there, whereas I couldn't reach the baby if needed if I was driving alone in the car and the baby was behind the driver. But is this safest?
But, my toddler is tall and his legs will be up against the driver's seat (compounded because the Summit seat back puts him quite far forward from the van seat back). The best solution would be to move him to a high back booster as he'd be further back from the back of the driver's chair, but he's not heavy enough for that switch yet. Do you have any suggestions or ideas?
We also have a secondary seat (an Eddie Bauer) which I could use instead of the Summit because I think it puts him a little farther back. But I would only use it while he needs the 5 pt. harness as it has been rated poorly to use as a belt positioning booster.

do you have a 3rd row at all? When my boys were that age we had a van and I found it was most convient to have the older child outboard in the 3rd row (passenger side) and the baby in the center/outboard position in the 2nd row. I could get them both buckled easily.
Now if you have dual sliding doors, I'd put each child outboard in the 2nd row. If you think you'd get a better installation with one seat, or have more room, as long as he's properly restrained in the 5 pt harness it doesn't really matter which you use. (Both seats are made by Dorel, aka Cosco.) Then get an inexpensive belt positioning booster (I like the Grcao Turbo Booster) when he's 40 lbs.

Yeah, my cousins with 2 kids each (we share babysitting for eachother) both find that puting the older child outboard in the 2nd row & the younger child in the middle fo the 3rd row to be easiest ... the kids don't mess around with eachother which makes it less likely anyone gets frustrated & when there are 2 adults in the car, 1 sits outboard in the way back next to the baby However, when their older kiddos have to use a booster, they sit in the middle seat of the 2nd row, away from the sides so mom/dad can see them in the rear-view better to know when they're not sitting still properly!

I have a Caravan too. If you use the non-outboard seat on the bench doesn't the seatbelt have to stretch way from the side of the van, making access to the 3rd row a major pain? Would that be a problem? I know on our van I needed my dd in the 3rd row for awhile, so I slid the rear bench up (ours has three positions) maybe if your son was in the third row on the passenger side, only slid up some, you could reach him easily to fasten his seat but he wouldn't really have anything to kick. AND I'm assuming you have 2 sliding doors, you could put the baby directly behind the driver. Just a thought, maybe that didn't even make sense, I better go have another OREO!!
one more random thought, IF this would help... I think I can move my 3rd row (3 passenger) bench forward to the 2nd row. I'm not sure how many people in your family, so these ideas may not work for you in the least! Too much rambling, need OREO!