Booking a Traveling ticket To Mexico

Hi all
First of all sorry if my topic in wrong place and i apologize in advance,
My Name is Mahmoud and I’m 30 YO, working as a technical support in network field In Vodafone Telecommunication Company.

I just wanna someone providing me with the easiest way to book a ticket to flight to my wife in Mexico/Guadalajara.
So I wish to get some support about “how to book a Ticket by Online/Agency” to flying smoothly without any problems at any airport and also the Ticket type that I have to book (Round Trip) and the shipper price.

Some peoples told me I have to by a Round Trip Ticket and another peoples told me ( you can only by Only one way Ticket ) is that true of not ?
Also he told me I have to booking the Ticket with less than 8 hours transit in any transit country to not asking me for a shingen Visa also I need to know if this info is wrong or true

PS: I need to know if I have to book Ticket (round trip) OR only (one-way) and please be notice that (our marriage contract is officially stamped Sealed in the ministry of Justice and ministry of foreign and I have a copy from the Mexican marriage contract that done at my wife city in the Mexican ministry government of justice there so my whole documents is officially and recognized and 100% legal .

so what is the basic info that i have to know first, and what exactly the necessary Document that I have to having there in Mexico in the future to having easy way to apply for any job opportunity and also what the most important document that I must have with me there to preparing it her in Egypt to take it with me.
So if there are any helpful member cans supporting me by telling me this details I’ll be thankful so much to him.
Thanks for all and waiting for response ASAP.
Regards,,
Mahmoud