Good Morning Bethany, and Welcome to Photo.net !
There are many great photographers here, with varying opinions and varying advice. Please take it all in and try to learn from it...don't get discouraged. There's also many threads about first time wedding photographers on this site...you'd do well for yourself to read many of them. They'll offer warnings and encouragement.
A few questions before I give any advice:
- What camera are you using?
- What experience, other than with Lifetouch, do you have photographing people?
- What experience do you have with weddings?
- Have you ever been a second shooter or wedding photographer's assistant?
- What is your plan if something goes wrong with your camera?
- What experience do you have shooting with on-camera flash?
- Indoor or outdoor wedding ceremony/reception?
- If the ceremony is indoors, is it in a church? If so, what are the church's rules regarding flash photography?
- How close are you to your friends that have asked you to photograph their weddings?
I believe that you have good intentions, but many of your statements lead me to believe that you are not prepared to do these jobs:
I don't have a spare camera. I don't really have an assistant.
You need one, but not the other. Assistants are not necessary - you'll find many of the photographers in this forum that do not shoot with assistants. You DO need a second camera - one you're familiar enough with to shoot under high pressure situations and make sure you get the shot. Do you know anyone that you can borrow a camera from? Preferably the same system you are currently using. You need a second camera - even if you don't shoot with it - just in case something goes wrong with your camera. (You'll also need spare batteries for both cameras)
I have researched poses and what to do since I was asked about four months ago.
Research is not the same as practice. Over the past four months have you practiced with real people? Have you been to a few weddings to see the basic flow of the day? Have you shadowed a wedding photographer, worked as a second shooter, or assisted? You can't learn everything from reading - you need to practice, practice, practice. Wedding photography is high pressure and there's no do-overs. Have you done everything in your power to really get prepared for the day?
I'm thinking about purchasing the 18-105 zoom lens. I have the 18-55mm and 55-200mm, but I don't want to keep changing lenses.
The 18-105mm, much like your 18-55 and 55-200, are not the best lenses for low light. They're fairly slow, and unless you're very proficient with flash photography or have a set of studio strobes you can set up at the wedding and reception, you'll be wanting for more light or shooting at very high ISOs. Faster glass is usually recommended for weddings, but with the right flash setup, they aren't necessarily needed. Stick to your two lens setup for now and change lenses when necessary. You'll likely be finding yourself shooting the 18-55 more often than not.
Do you guys think that lens would be ideal for the weddings I will be photographing?
No - I don't think the 18-105mm f/3.5-5.6 is even close to ideal. Everyone has their own opinion of what is ideal. Mine is a 17-50/55mm f/2.8 (DX) or 24-70mm f/2.8 (FX) and 70-200mm f/2.8 with a selection of fast primes (choose between 24mm/35mm/50mm/85mm f/1.4 or f/1.8) for really low light. My personal favorite is two cameras with 35/85 combo and a the zoom in case I have limits on my movements.
Also, what flash should I consider purchasing? I have been researching and researching and can't seem to decide.
Again, research doesn't tell you everything. Are you comfortable with manual flash or do you want something with TTL metering? Not knowing if you shoot Canon or Nikon I don't know which flash to suggest, but I recommend sticking with your camera manufacturer's brand for full compatibility and ease of use.
Finally:
Just recently I have been asked by two friends to shoot a wedding in May and July of this year. I accepted the offer knowing that it would be a challenge.
I'll ask again how close you are to your friends. Are you 100% sure you are up for the challenge? Are you prepared to lose your friends if things don't go well? (I ask because it has happened - search these forums) Have you prepared your friends for the results you can give them without setting their expectations too high?
You have five months to prepare (and have already had four according to your post). Do everything you can to get an assisting job and maybe even a second shooter position with a local photographer. Go to as many weddings as you can to learn how the day progresses. Keep an eye on what the photographer is doing and try to learn everything you can.
Nine months is a long time to prepare for your first wedding...you've got five left - start getting ready now!
RS