I didn't find timing to be that big of a deal. Personally I kept the same number of steps, just because it made more sense to my head. But yeah, you're most likely going to be pretty slow, so a Rocket will be way too much ball to begin with. I'd also suggest a Pitch Black.
Basically take it slow and don't force anything. I found solace in knowing that anyone switching hands isn't supposed to be any good anyway, so I never felt any pressure to progress up until recently, but that was more self imposed. You're going to need time for your bowling muscles to develop, plus you're also going to need time for your coordination to develop too. Also, the left side is a bit different from the right, so let your eyes be your guide, don't try to mirror everything. Some things are similar, some aren't, so just take it slow and easy. Focus on mechanics, and you'll build your way up just fine.
I also found it helpful to do as many other things as I could lefthanded just to build coordination, and found it interesting that a lot of coordination is the way your head processes and thinks about things. Some of it is muscle memory, but I feel like more of it is the perspective you see it from. The more you get your head to think lefthanded, the easier and the more quickly coordination will develop, in my opinion at least. Good luck, it's a lot of work, but I find it to be more rewarding. Small successes lefthanded FEEL bigger because of the challenges present, and yes, some of that comes from the admiration/support of other bowlers. The support and encouragement from other bowlers actually helps a lot.