McCreed's said it all really. You'' get finish all over the frets but that will sand off, after which you just go up the grits getting finer and finer until you're ready to polish them and make them like new.
Quality level is down to time experience and how much money you are willing to expend. The kit woods aren't the best quality woods out there - you aren't paying anywhere near enough for that, but they are certainly on a par with Squiers.
Due to ash dieback affecting so many trees, getting good quality ash is getting really hard, so whilst you may get an ash body or even an 'American ash' body, unlike a few years ago, you are unlikely to get a body made from dark ash with the grain lines far apart and all swirly as some of the kit pictures show. It's more likely to be white ash (if American), or another variety if not, with grain lines a lot closer together and a lot straighter.
If you want to duplicate the general look on an RS440, then a solid colour will be most suitable, so the grain pattern doesn't really matter that much.
Finish is all important if you want it to look like a bought guitar. Getting a good finish takes time, and there's a lot of sanding preparation and getting things smooth before applying the finish. It's not something that you're likely to get perfect on your first go, but it can be done.
Upgrading parts can certainly help improve the looks and new pickups will improve the sound, but the cost quickly adds up. You can certainly make a guitar that is as good as, or probably better than, a good Mexican Strat from a Pit Bull kit in look and feel and sound, but you'll probably spend just as much as you would as if you'd bought one. And it's resale value will be far less. On the other hand you've got a unique custom instrument that you've tailored to your requirements.
I made this Strat from a GST-1 kit for a friend who needed the MIDI pickup in it and he's pleased as punch with it. I personally don't like the colour but apart from that I think it looks lovely and it plays and sounds better than most Strats costing twice its final price (and 1/5 of that was down to the MIDI kit and extra bits needed for that).
That was my sixth build, but my earlier builds ended up quite similar in overall quality.