Oh, I'm so jealous! I would really love to have either a Kwanzan Cherry or a Yoshino Cherry. Did you buy yours locally or direct from a grower? How big is it? Was it expensive?
I like that you planted it to mark a special occasion. I may be doing the same thing because my baby is 6 months old and it'll be about another 6 months before we've landscaped the part of the yard where I want to put it.
Most ornamental cherries are shallow rooted and must not be planted too deep into the soil, (you will see the mark at the bottom of the trunk where the soil level has been, dont put soil above this mark, also dont like in an area that is too exposed to the wind and other elements, you dont say how steep your slope is, if it is a very slight slope you should be OK, if a steep slope, I would find another site, soil will wash downward and leave the bottom of the trunk bare, you will require to have stakes put in till the tree gets well established pos 2 to 3 years, make sure you keep checking the stake ties that will be attached to the tree, as you dont want the bark to be damaged OR too tight as the tree grows, also IF you have problems with rabbits/ deer ect, they love to gnaw at the bark and this lets desease into the tree, it might be worth your while to get a tree guard that will expand as the trunk grows, or make one with chicken wire 3 stout sticks in a triangle shape about a foot away from the trunk, to keep anything away till the tree settles in, and the young bark toughens up, since these are not cheep trees and you want it to grow with your child, get back to where you purchased it and ask for full likes and dislikes, I think I am right by saying the tree you have originated from Japan and they have cold winters but NOT a lot of STRONG winds, in Scotland, we always plant trees in october/november while we still have a wee bit of heat in the soil, OR, wait till early spring just as the soil starts to warm a little, that way the trees are not working to put root down AND find water all at the same time, as they get parched in hotter weather, most trees take in water as they come out of the dormant season and store it in the trunk till it is needed for producing leaf come spring, they do need water in hot weather, but most will have reserved enough, however, a young tree has not got the capacity to do all that on it's own, like your little daughter, it needs the right home, the right attention and lots of TLC till it can do things for it's self, so good luck, hope this helps a little.
Prunus serrulata is a big fan of the sun. However this time of year is always tough for new plantings (Fall is the most recommended). Anyway, i think any spot around your house that is not facing north will be a wonderful spot for your cherry. Remember that this is going to be a specimen planting so nearby flashy plant could possibly dilute the beauty of your tree. You want to make this a focal point, this is a tree that can really give some curb appeal in the spring. I would probably do a nice front yard planting with a possible stone/brick border, and then maybe surround it with some lowgrowing perennials or annuals of your choice. You have made an excellent choice, just make sure your water it everyday for the first 1-2 weeks and slowly ween off as the root system begins to establish. Also make sure to use a fertilizer that has higher potassium and phosphorus percentages (the last 2 numbers on the bag ie. 2-24-12). These essential elements will help your tree get started off right. Nitrogen is the first number but it is mainly for vegetative growth (great for lawns), and right now you need to focus on your roots. Also make sure that your hole is the depth of the root ball, but twice as wide. the original ground level can be located on the trunk, and if the trunk gets submerged by soil and/or mulch it could create a moisture issue on the bark allowing fungus and pests the innoculate. Back fill the hole with a humus, sphagnum, original soil, and fertilizer mix(not equal parts please read the label on your fertilizer bag before dumping it in the hole:)and the new roots will have a easier time getting spread out. You will probably not see any major new growth this season, but next year your kwanzan should be well on its way.