I soon will be going for my Private Pilot check ride. I would like to follow a curriculum similar to ATP flight school but do it at a FBO. What should I be working on next after I get my PPL?

Instrument.

That would be my vote too

How many hours of solo x-country should I have before i start my instrument rating? The instrument rating requires a total of 50 hrs PIC.

If I wanted to get 100 hours of multi-engine time on the way to getting my commercial then at what point should i start my multi-engine training?

Assuming you get your PVT in around 50 hours, you then will burn up about another 40-50 to get your Instrument....that gives you an estimate TTL 100 hours, with PVT & Inst Rating.....

Then right after that do your Multi-Engine, (you will do 1 check ride and get your Multi Engine and that includes instrument rating with it, since you will already be insturment certified).

Now you burned up about 15-20 hours of ME time for the rating above, that's a TTL of 115-120 hours...You must have a total of 250 hours to get your Commercial, so that still leaves 130 hours.....save the last 20 hours for the Commerical Mulit-Engine Standards Practice.....so that leaves you with 110 hours to burn up.

Keep in mind you might want to save about 5-10 hours off that time to burn in training for your Commercial Single Engine.

As you can see you still have the "extra" room to get your 100 hours in after your instrument, plus you save a check ride.....Also after you have your instruments it will free you up on some scheduling flexibility issues when the weather kinda sucks....

I don't have a lot to add with all of the good advice given so far. I just wanted to say, don't think of the time between instrument and commercial as time 'to burn'. It's a gift; you'll have an excuse to fly anywhere you want to. Some of my best flying memories are of that time.

I tried to make all of my "extra to burn time" by doing long cross countries in VFR conditions, like Sept/Oct, the farthest was from KLAL-KRDU with a fuel stop in between, took some friends, spend the night with family in RDU, was a BLAST.......

Do stuff like that, I don't know where you live, but take a 3-4 hour VFR flight to a major city, (you'll have your instrument so if weather gets kind crappy you can keep flying and fly around/over it), get a hotel, and goto a MLB Ballgame, or College Football Game, or something like that....make it fun, better remember no drinking!

I'm pretty sure you need 50 hours of cross-country time to take your Instrument ride. Also, under your plan, you will have Commercial Multi Instrument and Private Single IR. If you ever plan on flight instructing, or banner towing, or aerial photography, then you will most likely need that Commercial Single certificate. Actually, you will if you're going to get your CFI and instruct. Most people don't get to jump straight to MEI. Way too expensive.

If you want to fly for a living you need multi time. A great way to do this is getting your instrument in a twin. So, you'd get your PPL MEL next and then you can log multi PIC by getting your training in an Apache, Dutchess, Seminole, etc.

I do want to fly for a living. That's why I mentioned I wanted to train in a structure similar to ATP flight school. I believe if I do what Slice mentions above then I can get the required X-country 50 PIC hours needed for the instrument via my Multi rating.

I called ATP and they said they do a Private Multi rating (9 days) followed by a Private Instrument (26 days) and then followed by nationwide X-country. ATP couldn't answer where the pilot gets the 50 hours PIC X-country time for the instrument rating. Do those 50 hours PIC X-country time come mostly from the Private Multi rating? How many hours of PIC X-country time typically come from working on the instrument rating?