I am wondering about the process for hiring a MUA for a wedding. 

Is it expected to hire from their portfolio only or is it acceptable to request an interview of sorts where the artist dose my makeup to ensure that I like their skills??

You can certainly hire someone solely based on their port but that is a big risk.  Most look through ports and find one or more they like and then arrange a makeup test where you can discuss your expectations and do a trial run or test of the look. This test is usually paid and rates for tests vary.

Bridal makeup routinely involves a test with the bride.
There are several factors the makeup artist will want to establish before "the big day".

Tests are a routine part of the negotiation, and  do recommend hiring a makeup artist who does bridal as it is a event work different cup-o-soup from studio work.

Try to get a referral.  If you have a regular hairdresser ask them if they know someone.  Yes, you can ask for a trial personally  I have been hired without providing one.  It depends on if you are doing a destination  wedding or you are pretty laid back.  Remember, you will pay for that trial.  R-

I like meeting and doing a test with a make up artist before the wedding.  I look for good makeup skills but I also look for a cheerful calming personality.  Most weddings are a little hectic and sometime we get time crunches and crying brides and I like having a mua that stays calm and cheerful under stress.

referral and test makeup is recommended.  Doing a test is important because sometimes even if a makeup artist is good and highly recommended, it might not be the look or style the bride is looking for.

Agreed with everyone: DEF test! I always provide my bridal clients with a trial. Depending on your artist, the trial price may be taken out of your total fee. (Ex: if you are paying $500 for everything, but the trial is $100, you only pay $400 later.) Some people charge separate fees from the day of. I usually take it out of the total sum, just to make things easier. You may want to do a trial with more than one makeup artist, too. See which styles you like most, which makeup lasts the longest, etc. Good luck!

Thank you all so much for the advice I really appreciate it.

Is $500ish the normal range for wedding makeup and hair!?!   
Sorry if that's a silly question but I truly am clueless about wedding stuff..

Rates vary with location and by artist. In general...you get what you pay for. Top artists charge more because their services are in higher demand, their experience and skill level is greater, and they are better able to deal with the unexpected things that always arise during the big day. This is not an area you want to try and save money on. After your wedding all you have is photos and how you look in them. An experienced artist will be able to ensure you look good in photos and in person, no easy task. Just be sure their portfolio reflects that they are as experienced as their rates reflect. $500 is not at all unreasonable for makeup and hair for a bride if the artist is experienced and skilled.

All professional makeup artists who do weddings--who I have encountered--will highly recommend or even require a test before the wedding. Expect to pay for this. Many offer packages that include test makeup, day-of makeup, and maybe a few other perks.

I'm of the opinion that it's better to get separate hair and makeup artists, simply because that way you don't have to worry about choosing a makeup artist you love with hair skills you don't love quite as much, or vice-versa. Pricing will, of course, vary based on your location, the wedding details (day, time, season), and the demand for the artist in question.

Good luck!

Contact the ones you are interested in and discuss/negotiate with them.

Trial runs are standard for the industry. It is best to do a trial run since as amazing as an artist may be not every artist is the right fit for every bride. Many artists will bundle trial and day of services