I dont have time to read through all the replies, but heres what you need to know (off the top of my head, might be missing some things, as its been a few months since i got my j35 running)
1) motor isnt going to fit unless you buy a new k-frame
2) the ecu you have is useless, unless you plan on using a j35 auto tranny
3) assuming you want to go 6 speed, you will need either a 03 cl-s trans, 03-07 av6 trans, or a 04-08 acura tl transmission. $600-$1500 depending on the trans you want. if you go with anything but the cl-s trans, you will have to get the shift linkage pin re-welded or else your shift pattern will be upside down.
4) youre gonna need to buy engine mounts since none of yours will work so tack on $300-400 depending if you go aftermarket or OEM. you will have to buy the transmission beam + transmission mounts oem as there are no aftermarket solutions for that (not that i know of anyways.
5) youre gonna need richies harness ~$500, then youre going to have to get the key programmed to the ECU
6) youre going to have to run v6 axles. depending on the splines in the 4 lug hub... you probably wont be able to keep the same hub. so you will probably have to do a 5 lug conversion. soo $cost of hub swap + $200-$300 for axles
7) youre going to need a completely new exhaust system. if your motor came with headers you can reuse the j-pipe, but if not... you will have to get some aftermarket headers + exhaust... $xxx.xx
8) IIRC the firewall holes arent 100% the same in the i4 and v6... so you may have to custom route some vaccum lines, power lines.
9) battery tray will have to be relocated as it is on the drivers side on the v6's and its on the passenger side on the i4's.
theres my 0.02... i know theres more misc stuff im missing, but i cant think of them right now.
honestly, youre much better off selling the motor you just bought and just boosting your f23, or do an h22 swap. a full J-series build, although is nice can end up costing more in the end and be more trouble than its worth... esp if your chassis wasnt made for the motor itself.
feel free to correct me as i could provided some mis-information.
