It's a matter of negotiating. May be you will be able to find sellers that are not in a rush to move but need to sell. You can work out a lease back where you can buy now and they lease from you until December. They may be building a house, haven't found the new place etc. As you see it's all property specific.
It is never too early to shop for a house, especially if you are doing it for the first time. You probably want to go and look at homes too so you can have a better idea of what you get for your money. Investigate neighborhoods etc...
1. Get prequalified.
2. Determine where you want to live, perhaps even down to specific neighborhoods.
3. Start driving the neighborhoods so you get a feel for the prices and condition.
4. Start looking inside the houses about 3 months before you want to move. Contract 30-60 days out.
5. Looking now is typically disappointing as the homes for sale now will typically be sold by the time you are ready to move. The homes for sale then are not on the market yet.
If you go with a new home builder it will take 3 - 7 months or more to build so now would be a good time to start.
Depends on how motivated the seller is to sell their property. They may be willing to do so. Let's say you find "the home" in July and, as is typical, close within 30 days on/after August 2. You won't have a payment on the home due until October. So, you would just need to be concerned with Oct - Dec payments. So, realistically, what would those be? Is there an early release clause in your lease? Can you terminate it if you're buying a home? Some of the larger rental companies will allow you to do so.
Are you going to only consider re-sale homes? If you consider new homes, it could be longer before they're ready. The market is on sale right now. For example - this is from the Dallas Morning News in the last part of May: The Dallas housing market lost more ground in the latest gauge of U.S. home prices. Home prices in March fell 3.3 percent from a year earlier in Dallas, according to the latest measure from Standard & Poor's Case-Shiller index. We're also not sure what interest rates are going to do later in the year?
Happy to help,