Just like any breed there are stereotypes and exceptions to them.
As a generalization Percherons, like most drafts, are more docile and easy going than your hotter horses like TBs and Arabs. Now, depending on the breeding of the particular horse you can also have different temperaments. Many MODERN percherons are only a couple generations from full arabian on both sides so you can have a horse that looks like a gentle giant, but acts like a hot arabian. Percherons before being turned into "Drafts" to be used as field horses were war horses. Percherons are quite commonly used for carriages as well because of their beauty and refined movement.
The Percheron Horse Association of America is VERY strict about registrating, breeding, and transfering horses. So, if the papers are properly processed you can be sure you're getting an actual Percheron.
Percheron Horse Association <--the PHAOA website has a small section that talks about the disposition of the breed.
In general I've found most full blood percherons to be extremely intelligent, surprisingly sensitive, and very sweet.
The biggest problem I've noticed in crosses is when the SIRE is the hotblood and the dam is the draft. (I'm not basing this on nothing I've owned one and have known of goodly number of others.) I don't understand why it would make a difference or even if it truly does. Of course you aren't asking about a cross, but I just figured I'd throw that in there.
If I were you I'd try to get out and meet the mare at a show or trail ride or somewhere other than home, just to get an idea of how she responds to new stuff, new places, and new horses.
As far as riding they're wonderful (again each horse is different). They are noted to be wonderful movers, though some have quite a bit of natural knee action (which is great for hitch, not so great for hunters/dressage). They have fairly large strides as percherons are usually rather leggy, so if you're used to your stereotypical QHs you might feel as if they're rushing at first.
Also jumps are great, because you're already high up so the jumps don't look as tall

Good Luck

laissez faire, laissez aller, laissez passer, et laissez les bon temps roulez toute la nuit!
www.phyxiusphotos.com Christina Dale Equine Photography