Booking really isn't that hard, you pick your resort and decide on your dates and call CRO and make a booking......
Though we never use a TA, maybe for your first trip it's advisable...but finding a reputable, well versed in WDW knowledge is hard to find...alot claim to be, but aren't...good luck on that one....
We're not package people, prefer room only reservations (only have to put down one nights deposit to book) and get a better rate with room only discount (general public or AP)..packages include things we're not interested in or going to use...so no sense wasting our money (others like it becasue it's all there and under one price...and sometimes involves free dining (which we're not interested in).
Best thing is to pick up a travel guide to WDW, do some processing of meals and prices of things, send for the free DVD from Disney and see what your pocketbook warrants....length of stay.....days in the parks etc....then when you get a feel for the amount of cash you're going to layout with what you picked and want to accomplish....find a TA and have them give you a quote....compare and see what's what...we always book our travel separate...
Check mousesavers.com for discounts out for your time period, you can book now and when a discount comes out, you or your TA can apply it to your reservation...but remember, with a TA, they own your reservation and if you want to make any changes or cancel alltogether...they have to do it...you can't call Disney and do any of that....
Hope this helps, good luck on that first trip...they are always the best....