I always order my vehicles. I don't want a truck that's been sitting on the lot getting acid rain on it and being driven around by who-knows-who. Especially in the winter months, test drives are quite messy for the interior. Anyhow, to answer your questions:
Yes...you are only going to be able to order through a dealership. To get your best price, you going to want to have one "spec'd out". Go on Ram's website and build one exactly like you want it and document all those options. You can now present this "spec" to all the dealers, and it will allow you to compare apples-to-apples when it comes to price.
When requesting your price for your spec'd truck, ensure that ALL dealers are giving you a price that's PRE-INCENTIVE. Since the incentives that will apply are going to be those that are available when the truck arrives, they may not be the same incentives available today. With that in mind, you want the PRE-INCENTIVE prices from dealers. The incentives will be what they are when the time comes to take delivery of the new Ram.
Get prices quotes from numerous area dealers to get your best price. I got prices from 21 dealers. Luckily the FCA brands have dealers all over the place, so they will need to fight for the sale a little. The truck I ordered had an MSRP of $68,690. I received dealer prices ranging from a high of $62,616 down to $59,396 (that's a $3220 difference in dealer pricing....which is huge to me). Whatever the incentives are at time of delivery will come of that final number.
Your trade should have NOTHING to do with the new Ram cost at all. That's a math games dealers will play when they know they can. I generally get my best new vehicle price before even talking about a trade at all...as it's a separate issue. In the end, the dealer you choose may be $300 in price higher than your lowest new-truck price, but they may give you $500 more for your trade...so it'll be a combo of the best deal in the end. Since you are ordering the truck, it will literally be the exact same truck (to the VIN number) no matter whom you buy it from.
Some orders take longer than others with no rhyme to reason. I ordered a Limited the last week of February. As of today, this past Tuesday, it's already been built and is waiting to be loaded on a truck for delivery to the dealer. That's pretty fast. I've seen records of orders that were placed long before mine and those folks are still waiting for their truck to be built...and I can't say why.
Also...after getting close to ordering, make sure you go to Ram's website and request a PRINT brochure. It will take about 2-3 weeks to get it, but your name will be registered in their system. You can then call their incentive department at 800-227-0757 (option 1) and get a special rebate code that's good for $500. You provide that to the dealer when the incentive paperwork is getting done. From the time you register with Ram, you have like 3 months to call-in for that code...so don't get a brochure now if you aren't going to buy for a while.
Another incentive that's not listed on the website is 38CK5. It's a $1000 conquest incentive if you own a Ford or Chevy truck now. You don't even have to be trading it in...just prove that you own it. Ram has been renewing this rebate for quite a few months now. It will expire at the first of the month, but will most-likely be renewed again.
Anyhow...I think I've answered everything. Hoping to hear that you get one ordered up.