Here is your three minute overview of the decision process:
If you travel to Disney pretty much every year and like to stay at the nicer Disney Resorts, then yes, buying DVC makes a lot of sense and will save you a lot lodging expenses over the long term. However, most find that they simply start "upping" their vacation habits due to all the savings. This translates to buying MORE points and/or traveling to Disney MORE often. Thererfore, be aware that a DVC membership may not necessarily decrease your Net Disney Vacation Expenses.
DVC is not the only way to enjoy regular
Disney Vacations. It may not even be the best way. It is simply one way to do it. You could also simply put that cash in a high interest account and draw on it each year and stay wherever you want. You could also buy a much less expensive timeshare in the Orlando area (there are many nice ones, many very bad ones) and use that each year.
If you decide to buy, don't base it on any perks or "incentives", base the decision soley on your intended travel habits and wants for the next couple decades.
Buy from DVC directly if you want a smooth and easy and quick transaction or if you need easy financing (careful with this one, that adds a lot of cost to the picture). Buy from a reseller if you want the best price and don't mind wating 6 weeks or so for paperwork issues.
Buy at a resort that you like. You many not always get in at another resort during your travel dates, so you want to make sure you will enjoy the resort where you have a booking advantage. I would not advise buying at a resort that you would never be happy staying at. However, in general know that except for high demand times or high demand specialty unit types, you will generally be able to use your points at any of the DVC resorts so don't stress too much over home resort.
Use Year is way over thought, especially by new people (I was one). Use year does not determine when you can make reservations. It only sets certain timelines for bankinig and point expiration. In general, you want to have a UY month immediately prior to your normal travel dates. This is so that if you need to change/or cancel a reservation, you still have most of your use year to use or bank those points.
If you have no specific time period as a preferred travel time window, then UY really has no importance as your reservations will be throughout the year. Also, remember that over 50 years your schedule and travel habits are likely to change, so don't stress over UY.