TWH are known generaly for thier good dispositions BUT they are horses none the less and with varying personalities. Not all lines of TWH are gentle and even tempered. They are generaly easily trained and generaly put up with alot of stuff. Notice how I use the word Generaly. This is a broad statement that covers the entire breed not individuals. Just like one can generaly state that Arabs are hot, highstrung and flighty. However there are those that are very even tempered and great mounts. Some ppl like them hot and a little high wired. So its alsol in personal preferences.
I will also state that a good horse has no colour and no specific breed as long as its suited to your level of equine education and riding ability. I do fancy TWH because of thier noted temperments and gaits (and physical characteristics) but I have worked with some that were handfuls. I have also worked with Arabs, TBs, QHs and Warmbloods (amonst others). Generaly I do not care for TBs but I will not knock them entirely out of mounting choice if I found one with a good temperment, quiet disposition and so forth. I rode an ex racehorse in WP classes (only walk trot classes because he would not and I mean would not take his right lead.).
If you like TWH becaue of thier gaits then look for one that is wel trained, get an instructor that is well educated in TWH and thier gaits to educate yourself on. There is alsot of misconceptions on how one rides a TWH or a gaited variety but they are just that misconceptions. I do not find that much difference in the way one rides a gaited variety over other diciplines as long as the rider is well centered over the horse and is in balance with the animal and knows the difference in thier various gaits. You can most definitely canter a gaited horse, I do. In shows (depending on the show) most do not canter them unless specified because its the specific gait that is looked at and is emphisized.. Pleasure riding though, one can gallop over the meadows if one wants with a gaited variety just like with other breeds. Its not going to ruin the gaits. I have let my gaited TWH that perform the true runwalk or rack rip it up (full out gallop) from time to time on a flat way or an open ranged area. As long as you know how to ride then you should have no problem asking for them to come back down and gait again (once its been established). Getting some good solid instruction is important either way you go. Picking out a good solid animal that is trained to your level is also important.
A sored animal can have lasting problems depending on the severity of such. Mostly its the lasting scars. Sometimes hooves can have ever lasting effects depending on how badly they were damaged. Joints can also have lasting effects esp on the performance (stacked up) varieties depedning on age, length of time used and conformation, etc like calcium deposits on the joints and arthritis and joint degeneration. If you plan to show even at low level in the future the problem can be the scaring. If you purchase an animal that has been sored and has ever lasting scars from it a DQP can disqualify you in a sanctioned show for having scars even if you where not the one who caused them and are old. Somtimes Vets will verify this buts its no guarantee. Depending on the type of soring done (like stewarding) will depend on psychological issues from such. This can be an everlasting problem but most times is managable with retraining. Scars from previously sored animals that are superficial (skin deep) wont be a problem if they have healed and are the animal is used as pleasure or in a dicipline that does not require a DQP present. Sometime hair on legs will remain wavey or missing in heavily scared areas and may even turn white but functionaly are fine. Farrier care differs from animal to animal just like in other breeds. If you are looking for a smooth gaited one sometimes feet are trimmed according to the gait and its problems buts its relative and a farrier should still be well knowledgable in hooves and in balanced hooves.
OTTB need to be retrained and this can be a task esp if your not educated enough on how to do this. Some do great in other diciplines and excell in them, some do not. Re-educating a former race horse is not for the faint of heart.
Take your time, explore your options, try out several horses including gaited varieties (not just TWHs) and see what your fancy is. You might be suprised. Happy hunting.
"The question is not, can they reason? nor, can they talk? but, can they suffer?" Jeremy Bentham