[myTouch 3G, Magic General] mumilover:
Q1) Yes the spl is optional. When newbies (which are the main target of the guide you linked too) come here, they are looking for an easy upgrade. Playing around with spl and such is not a good idea, unless you do your research... Sadly only 1 out of 100 do that. That's why the custom recovery is a perfect solution. You really have to do some stupid **** before you COMPLETELY **** up your device. Plus you can do almost anything using custom recovery.

Flashing a spl ( as i write in my guide) is only valid if you know some shell commands, know the difference between img and zip files, plus understand how the device is build around the different partitions, e.g. radio, system, misc ect. Sadly only few uses the time to understand the above and we have like 1-3 every day crying for help.

SO - only flash spl if you know what you are doing or have done the research.

Q2) There are no custom radios. Only stock. For your device, the 32A or more correctly the CPLD-12, there are 2 different combos of radio/spl/recovery you can use.

Read around for more info as this has been written like 100 times :0)

Q3) Well, it depends :0)

If you play around with spl or radio you can brick your device. Again to understand why here is some simplified info.

Spl - Secondary program loader - is the data that has to be loaded when the device wakes up. When you push power button, the hardware wakes up, and follows VERY SPECIFIC steps to activate all the internal components. When it's semi done, it goes for the spl to load the rest. The spl always has to be on the same place or the device will not know where to look. The device is like child(which is born again every time you hit the power). When you hit the power button, it have some instincts(the steps) then it gets more and more intelligent as time goes by and more and more data is been loaded and processed. Think of the spl as the first part of computers BIOS. When the spl loads, it has to get some info about the complicated hardware, like the screen, antenna, sound ect. That's what the radio is for. So the spl has to know WHERE to look for the radio, and the radio has to be in a certain format or the spl will be confused. Remember, we are very early in the loading process of the device, so the data is very machine-close and in a very specific format.

When the spl is done, and the radio has been processed, then it will look at the boot partition for info on how to load the OS. The boot partition has info about how to load the OS and the different partitions, e.g. userdata, system ect. It will also try to load the kernel which is the CORE of the OS. It handles the ram, filesystem, I/O, mount of sdcard ect.

BACK TO THE POINT:

If you mess up the first part (spl or radio) then your bricked. You device is like a 2 week old child and is useless. It wakes up, poops on you and sleeps again.

So, DON'T **** UP THE SPL OR RADIO.

If you mess up the rest, you can still recover the device. Some times that can be very limited because of the perfected spl, but that's for another thread :0)

So, for your device, follow my guide and you should be good to go. If you are confident, then flash eng spl also :0)

It's up to you to decide....

Good luck