Need timeline help asap..

The first thing I noticed is that you have 30 minutes for first dance and speeches. That is way too much time. First dance and speeches (these should actually be toasts not actual speeches) should be 2-3 minutes each and you shouldn't have too many people speaking - 3 or 4 at the most. Also, guests shouldn't wait 45 minutes to eat dinner.

The second thing I noticed is that you did not give your guests enough time to get their food and eat. You should allow at least 1 hour for dinner especially since it is a buffet. It will take a while for each table to get their food. Plus you need time to do your table visits. Usually you and the groom will eat first and then go to each table to visit while they are eating. I had a plated dinner and it was 1.5 hours. We did the toast while people were finishing dinner and then cake cutting immediately after dinner. We then did our first dance which led to us opening the dance floor for the night.

The next thing I noticed is that you have 15 minutes for spotlight dances. This is also too much time. No one really wants to sit there and watch you dance for 15 minutes. Not sure how many spotlight dances you're having, but try to keep these to 2-3 minutes and consolidate them if you can - parent dances at the same time or remove a dance.

Last thing I noticed is the time for the cake cutting and serving the cake. You don't need to serve the cake immediately after cutting it. We didn't. We cut the cake at 7:45, had our first dance at 7:55, opened the dance floor at 8, and then the servers served the cake at each place setting around 8:30 for guests to eat whenever they wanted as they took breaks from dancing. As far as your DJ questioning it, don't worry about him. It is common to cut the cake after dinner before open dancing (that's what we did). Some people even cut the cake immediately after their entrance and then serve it later.

One suggestion would be to do dinner before speeches. You then could have the speeches during dinner which I personally always like. It speeds things up a tad. Then you can do the "spotlight" dances right after dinner or towards the end of dinner. This then opens the dance floor. Then in the middle of dancing do the cake cutting. I would do something like this personally:
5:30-6 ceremony
6-7 cocktail hour and photos
7 guests enter reception area & get drinks
7:15 wedding party enters reception area
First dance
7:20 Dinner buffet starts

7:50 Toasts during dinner once everyone looks like they have gotten food.

8:15 - Spotlight dances

8:25 - Dance floor is open

8:45 - cake cutting & service.

In general, buffets are a bit more casual so I wouldn't worry too much about people eating throughout the night. I would be more prone to do things in the middle of food like the dances etc because sometimes they can be a bit awkward to watch. This gives people something to do so that they don't feel like they are just watching awkwardly. I think your DJ is right in cutting the cake after people have danced. I personally like to work off some of the yummy food before dancing - maybe get another drink too.

Hope this helps!