Welcome to SaleHoo! It's great to have you here :)
It's the perfect time to start since Christmas is fast approaching. Like what fudjj has said, for your initial contact, email would do. Note though that some suppliers have a backlog of support emails so it may take a few days for them to get back to you. In this case, it would be best to give them a phone call.
Also, note that no true wholesaler should charge you to sell their products but an exception to this are drop shippers. As previously pointed out, drop shippers may charge a small fee for every transaction to cover for packing, handling. There are also some that will charge small account set-up fees. While by no means ideal, this is a fairly common practice among drop shippers.
There are many possible questions to ask a supplier. I suggest that you ask everything that you want to know about them and their services before doing business with them. Some of the questions might have been answered already by viewing the supplier description in our directory or by going to the supplier website's Help section.
I have listed some of the important questions here for you.
1. What are your wholesale distribution policies?
2. What are your returns policies?
3. Do you charge a fee to set up an account?
4. Do you accept PayPal or credit cards?
5. Are the products stocked in your own warehouse?
6. Are you able to provide true wholesale pricing?
7. Do you collect Tax ID information?
8. Do you sell wholesale and retail? Do you sell on eBay?
Additional questions for drop shippers:
1. Are you able to provide a real-time inventory of your products?
2. Do you offer blind drop shipping?
If you click on the 'Education' tab on any SaleHoo Page, you will find some great article with excellent tips on finding suppliers, pre-qualifying suppliers, online selling, etc. Also, don't forget to download the Bonus Guides by clicking on the 'Bonus Guides *New*' link on the left-hand side of any SaleHoo page.
Hope that helps! I wish you all the best!