1. I understand 98-00 easiest 5.0L swap. What about '97, it's different?
a. The '97 fuel injection is low pressure (~40psi) and incorporates a return line; while the '98+ uses a higher pressure (65psi+) and doesn't incorporate a return line. There are also subtle differences in wiring, where the connectors and pin out are basically identical. Specifically '99-00 Rangers use the same PATS wiring - so you can plug the Explorer module into the Ranger wiring and it works. The '97 Ranger wiring is older generation.
b. The '98-'00 Rangers and corresponding Explorers both use the same front frame (more/less). While SLA versus TTB/TIB is part of it, it goes beyond that to slightly different engine mounts, radiator/ac condenser mounts. It comes down to the '98+ Ranger mounts are in exact right location, while the older ones need modification.
2. Something is different about the '97 front suspension that makes it more/less desirable? TTB/TIB etc.
This is more personal preference - in a nutshell TTB better off road, SLA better on.
3. If the 4.0L SOHC is better and it came out in '01 then should I look at '01 besides or is there reasons '01 sucks?
You should look for '04+ 4.0 SOHC - they have a stage better guides. (They should still be replaced at this point).
4. Is the 3.0L in those years more reliable than the 4.0? Seems like I read a lot about timing chain issues in the 4.0.
The 3.0 revs higher for its power band (So, does the 4.0 SOHC, but extra displacement helps it down low). People don't expect a truck to have to rev to make power (Dad hated his 351W as it was "gutless" the way he drove it compared to the 360 in his old truck. But if you downshifted and let it get some revs, it ran about the same). 3.0 doesn't lack power - you just need to get it up on cam to make power. If you do so, it rewards you with descent power, but burns gas like it is making that power.