Not sure on exact tempuratures but it may be best to melt in a double boiler. Wax can be explosive when melted. I have heard, and will try it on my mug,  to warm the leather itself as well with a hair dryer or some such. Not too hot, only as hot as your skin can handle then it won't burn the leather. This opens the pores of the leather and allows the wax in. I have had some problems with splotchiness as well and I'm not sure if it's the weight of the leather or some other factor. At Tandy they encouraged me to clean the leather first with something called deglazer(?) as leather often has a protective coating applied for shipping. This will open the pores and clean the leather so it will accept paint and wax easier. Never heard of it before this and haven't tried it yet but you may want to keep it in mind.

375 degrees is good.  Be careful not to go above this, as paraffin can explode if it's too hot.  Always wear heavy work gloves and eye protection.

Just as Daði said, test a couple of scrap pieces first.  When you put the leather into the wax you should see an obvious reaction.  Air bubbles should be coming off the leather.  Only soak the leather for ten seconds.  A really thick piece can be soaked for 15 seconds, but I would not go longer than that.

If you are going to drill holes and attach straps, it is best to wait overnight as to let the hardened leather cure.