If you book it in early enough you could get it done somewhere like MAC but you need to book at least a month in advance if it's for a weekend as they do get very booked up. Go in to your local counter and talk to some of the artists before you book, you can request someone specifically and everyone has their own style - although don't be put off if their make up looks a lot more dramatic than you'd like yours to look as, contrary to disturbingly popular belief, make up artists are not in the habit of making you look like themselves unless you specifically ask them to! (You'd be amazed at how many of us hear "Oh, I wouldn't want it like yours" from someone who blatantly has completely different taste to us)
If you have it done professionally it should last all day and well into the evening. All you would need to have on you to touch up would be lipstick/liner, transluscent powder and blotting sheets if you tend to get very shiny.
I would definitely not recommend Touche Eclat or similar for a wedding. Lovely for everyday use and works wonders but with the flash of the camera you will look like you've been on a skiing holiday in all the photos. Think, negative panda look! These highlighters are seriously light reflective.
If you want to do it yourself then, yes, I would recommend a primer. It will help the make up stay on longer. I would also recommend using an eyeshadow on an angled brush along the lashline instead of eye pencil if you suffer from smudging or panda eyes when you wear liner. If you like the make up smokey then just start off with foundation and powder around the eye area and then do the rest after your make up. That way you won't end up with eyeshadow all down your cheeks. Waterproof mascara is a must if you are likely to become emotional watching your best mate exchanging vows. Lightly 'scribbling' lipliner over the whole lip first will keep your lippy on longer
There are many good reasons to treat yourself (as a bride, if not bridesmaid) to having your make up done. Apart from the looking great aspect, it is a little bit of quiet, calming time to yourself. Having make up applied is very relaxing and can be a really wonderful thing whilst all the chaos is going on! Also, when you do your make up, it's often a tried and tested look that you wear everyday, or to go out for an evening but do you want to be wearing your everyday make up with a really WOW dress that you would never wear any other time of your life? You will be looking at the photos for the rest of your life so you may as well be really thrilled with what you see. The other thing to bear in mind is that, sometimes when you are nervous or excited and try to be painstaking about doing your make up it can sometimes go wrong (think about whether this happens to you when you go out somewhere special) and thus make you stressed or more nervous trying to correct it.
I am always completely amazed when people come to me for a trial after having had an awful trial with someone else claiming to have been made to look like a tranny, or really dated, or not like themselves at all. Like everything else, you should really research the artist and their work, as well as finding out about the way they work, before booking them. There seem to be 2 types of wedding make up artist,
a) the bad type, who seem to have a few "stock looks" for wedding make up and apply them to every client whether it "fits" them or not.
b) the professional and skilled type, who spends time talking to the client and finding out their personal taste, what they and their bridesmaids will be wearing, the clients' personality, recommends collecting photos of make up that appeals in advance of trial to make sure you're both on the same wavelength etc. Ideally, someone who works in fashion or entertainment so their references are a bit broader than just some dated idea of wedding make up.
As a bridesmaid, if you are going to have your make up done by the MUA who does the bride, you will not have had a trial, so if you have a particular way you like to wear your make up do tell the MUA. If they do your make up and you don't like it, tell them what it is you don't like. There are so many different ways you can go with make up and it is quite personal so it's helpful to know what you like. I had one bridesmaid get all upset because she didn't like her make up. I asked her why she didn't like it and she said it was too natural and pretty and she was a bit more of a 'strumpet' so I adjusted it accordingly and she loved it. No need for the upset! Another common misconception seems to be that MUAs are mind readers and that if we fail to do that we are crap. Communication is key 
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Here endeth the lesson.