Welcome to the forum and you've come to the right place for plenty of helpful and friendly advice!!
The Marlin Sportster is a great car to build and the finished car is in a class of it's own in terms of looks, handling and performance.
You can see my build pictures here...
http://www.flickr.com/photos/peters-...7631773598897/
Some advice....
1. Make sure you will have plenty of time as it's not a quick build. I built mine over a 5 year period so don't expect to build it for next summer!!
2. Talk to Terry at Marlin about future supply.
3. If your not sure about buying direct, look out for an unfinished kit. They are as rare as 'hens teeth' but do come up from time to time. Many kits do not get finished so do come up for sale, but don't pay over the odds. (speak to Danny Nelson at the MOC and keep a search running on ebay)
Do lots of research on which engine you want. There are many BMW forums that are a good source of info plus Wikipedia and Realoem.
http://en.wikipedia.org/wiki/BMW_M3
http://www.realoem.com/bmw/select.do
4. Buy a whole car that is running and make sure everything is working OK before you dismantle it.That way you know the engine is good and you can remove very last bit of loom and connectors that you need. (which is almost impossible when you just buy an engine and this can be a nightmare)
5. If you do buy an engine off ebay be prepared to find its a 'dud'. I've bought two engines off ebay and one was excellent and one was junk so it's very risky. You can go to a specialist breaker like FAB but you'll pay almost as much as a whole car.
6. Avoid e46 cars as they are the ones with fiendish electronics that beat me!! An E36 M3 would be the one for you with either a 3.0 or 3.2 lire engine.
7. Check out the IVA emission rules to make sure you buy the right year unless you want to install cats which can be expensive.
8. I'm not trying to put you off a Marlin but have a look at GKD Sportscars as they also use BMW engines and they are a good source of info, but the Marlin Sportster is a much nicer car to look at, polish and drive :-)
Good luck, it's a great car to build and you will never regret it when your finished!!
(I'm sure Patrick will be along with some pearls of wisdom, as he is our BMW expert!!)
...peter
P.S. also check out Ian's and Nigel's Flicker sites
http://www.flickr.com/photos/58068042@N07/
http://www.flickr.com/photos/marlinbuild