I'm guessing you're doing atp. How did you manage to have a full time job AND do your training? What would you do if they called you to work ?

One thing about part 61 is that you’ll be doing most of the ground school work on your own, just like at ATP. If you can’t keep up because you’re not good with non-structured programs or you can’t get the help you need to explain some of the information you’re going to end up feeling frustrated. Frustration can turn anything you’re trying to dip your toes in into resentment and you’ll end up abandoning it and wasting money.

At the very least start with part 141, it will walk you through the process, you’ll have instructors who will be there for you to explain things you might have already read. So it’s a like a double lesson. People are different, but nothing wrong with going over the same material from a different perspective. If anything, you’ll be a safer and more proficient pilot.

Some instructors also have enough experience to give you a lot of helpful anecdotes you won’t get from a 61 program.

Side note: Can taking a leave of absence reflect badly on you at your FA job? If so, why the rush?

ATP has a nice turnkey program, but remember that multi engine training is in Texas (or is it FL?) for a few weeks and once you graduate, you can’t request a base airport or city where you’ll be an instructor racking up hours.

It’s at ATP’s discretion and you’ll have to bunk with 3 or 4 other roommates. That might be something you’re used to as an FA (I don’t know), but if it’s not, then it’s something to take into account. The older we get, the less tolerable it is to have roommates.

I can’t help much with the flow programs since I don’t know much about them. But hopefully this information can come in handy in making your decision.

its a LOT more money than an f/a, and comes with the responsibility and respect of a command authority position. Slinging drinks will never fill the void if you truly want to be on the decision making end of the jet. Go for it!

If you're looking at ATPs I'd suggest you take a good look at some of the threads on here about multiple failures. ATPS has a reputation of sending students on checkrides unprepared. Training failures follow you forever. Get more than a couple and your dreams of working for a major airline are shot.
Wherever you go, become familiar with the Airman Certification Standards (ACS). It is EXACTLY what is on the check ride and what the expectations are.

I'm going to join in with the others in saying don't give up your F/A job until you have the PPL and maybe even an instrument rating. Bid minimal days on schedules, fly your rear end off on days off. You could do the LOA for a few months but with enough seniority you may not need to do that. I don't know if your airline has Continuous-on-duty overnights or not but those are great for lots of time off unless you commute. And if you have a long commute, the LOA makes more sense. Do NOT burn any bridges until you've got plenty of flying hours and are 100% certain you want to do this and have passed a checkride or two.

Thanks to everyone on the advice. I made up my mind and I will be taking an unpaid leave from my FA job for 2 months and join a part 141 school and take my private there full time and hopefully finish by the end of the 2 months and after that I will make my decison to either go back to work as a FA or quit my job for good and go for the rest of the ratings.

2 months is an aggressive timeline, esp for part 141. It’s possible though. Before you take your leave should do an online ground school and get your written test out of the way

I would be going to 5 lessons per week so I'm pretty sure I'll be able to do it in 2 months. This is pretty much all I'm going to do. Study and fly. Thanks for the tip regarding the online ground school. Is there a website?

There are a ton of options out there for online ground school, but the one I’m most familiar with is Gleim. You can order a Gleim PPL kit and get the books you’ll need to study, a far aim, a logbook and a flight bag for a pretty reasonable cost. I think it’s around $150. It also comes with an online ground school and written test prep.

The big deal with Gleim, is that once you complete the ground course it provides you with a certificate that counts as endorsement to go take the written test.

if you use a company that fails to give you an endorsement you’ll still need a logbook signoff from an instructor before you can take the test.

getting it done before you even start flying would be a major step towards getting your stuff done in 2 months. You’ll only have to focus on flying and will pick stuff up quicker after being pretty familiar with everything from self study

Double all the time and cost estimates the recruiters give you. A full-time student might complete the zero-to hero in 9-12 months in Arizona, where the weather is great. Anywhere else, weather is a huge factor and delay.
Be prepared for getting "signed off" to take your checkride, but the evaluator isn't avail for 3-5 weeks. Unless the school has in- house DPEs (evaluators), you can count on delays. And don't forget Mother Nature can cancel your checkride day. Or a maintenance delay on the plane. Or you get a sinus infection. or...you get the point.
I cancelled my PPL checkride 3 times for weather. My Instrument checkride was delayed 5 weeks waiting for the DPE; Commercial check delayed 3 weeks for the DPE. Multi engine delayed 4 weeks for the DPE. All different DPEs by the way. And you have to keep flying during those delays to stay proficient, which costs more money. YMMV, but this is how it played out for me.

Don't guit your day job until you have your PPL in hand. Then decide how to proceed.