1) It is legal to use photos of items they sell our suppliers?
Unless you are authorized to use manufacturer photos it would be recommended you do not.
2) Do You know, if there are suppliers to facilitate the integration of the products they sell to automate updates to my site? There are some suppliers that can do real time product statistics and inventory but generally that only works for them. Some suppliers may have CSS updates for subscribers but that is rare.
3) What are the best products to sell? That depends on who you choose as a dropshipper. If your trying to target the US market and use a US dropshipper such as Link hidden: Login to view then you should list as much as you possibly can on your website. Dont just pick and choose the most popular items as they will rarely sell on your site, you may do far better selling just accessories. The more you have available to sell the higher your chances of selling them.
4) What kind of Items do you recommend me to sell at the beginning? This is again entirely up to you. there is a market for everything. But the more you have on your site will greatly improve your chances.
5) What are the DropShippers that more reliable and with better prices? This will be found better with testing out various suppliers. Make sure you use quickbooks to track all the dropshippers you use. And use as many as you can to increase your available items. The best known Dropshipper I prefer is Link hidden: Login to view but there are many others out there.