I'm new to Pure data.. I want to make a sequencer for iOS which is something like Rebirth from propellerhead - the 808, 909 drum machines (I think I will have samples to start with) and a 303.. but with more polyphony so chords can be done.

Is Pure data ( PdLib ) in combination with objective-C for this a good idea?

Any recommendations where to start?

I'm planning to read this book that might give me some more inspiration and guidance
Making Musical Apps: Real-Time Audio Synthesis on Android and IOS
Peter Brinkmann

I know some objective C, C++, Java and allot of HTML5 with PHP/SQL stuff etc and been tweaking knobs on synthesizers for 20 years or so (since I was a kid).

Yeah that book is a good starting point, maybe look at prototyping first using MobMuPlat.
As for your drum machines, the sampler.oneshot help file in Pure Data/audio.examples might be a good place to start to make an abstraction for each voice.

That book is a good place to start, and that's about it. It's almost completely outdated as a good 3rd of it is dedicated to RjDj so those pages can pretty much be torn out and thrown away . The book also actually contains the statement "...but having a Pd patch output MIDI events only makes sense if the patch is supposed to control external MIDI hardware, such as a synthesizer. That is a rare use case for mobile apps." which was sort of ridiculous in 2012 when the book was written (there were probably a dozen iOS MIDI interfaces then) and is completely ludicrous now, as there are probably over a hundred, not to mention Audiobus, which I think actually came out late 2012. The good news is that there's surprisingly little you need to do to interface between Pd and Obj C and if you build the "GuitarTuner" app in the book you'll have pretty much everything you need to know from an Obj C standpoint.

All,

Is this the C# Forum?

Is there a Visual Studio Solutions (C#) for building and samples of Pure Data?

The book is a good starting point along with statement. It is very less use case for the mobile apps.

There's a C# libpd API, I'd imagine it's pretty similar to the Objective-C version @Zhah001