Well I can answer first two of your questions...

1) In route section, the order does not matter...so its correct

2) I know, using the SCRF=read keyword one can input data related to solvent...like dielectric constant. In Gaussian manual also there is a hint that other solvents can be used...but it is not clearly described there. You can ask gaussian help team for this. The portion of the manual I'm talking about is given below (it is part of SCRF keyword)

"The following solvent keywords are accepted with the SCRF=Solvent option. We list the ε values here for convenience, but be aware it is only one of many internal parameters used to define solvents. Thus, simply changing the ε value will not define a new solvent properly." You can read the whole part on

http://www.gaussian.com/g_tech/g_ur/k_scrf.htm

To study the the exchange between two structures (you probably mean conformers) calculate both structures and try to locate a transition state, which connects both structures. Afterwards you can run a IRC calculation to make sure both structures are really connected by the transition state.

http://www.gaussian.com/g_whitepap/qst2.htm

http://www.gaussian.com/g_tech/g_ur/k_irc.htm

http://www.gaussian.com/g_tech/g_ur/k_opt.htm