In April, I flew into Terminal 4 at Madrid. I bought my ALSA ticket online. Passport control and customs clearance took less than 30 minutes. It helps if you do not linger or sightsee.
If you walk briskly following signs. you get through the arrival process, quickly. My luggage (rucksack in a brightly colored laundry bag) was coming off the belt just as I arrived, about 15 minutes after I got off the plane.
The ALSA bus counter is outside the Customs exit, opposite, along the glass outer wall, and slightly to the left. The bus platforms are just outside, stalls 1 - 4. You can see them outside, beyond the ALSA ticket counter.
Personally, I advise buying the ticket online. I did so using Paypal for payment. This allows you to proceed directly to the bus, no need to stop at the counter. There are displays above the counter clearly explaining arriving and departing buses. The line at the ALSA counter can be long and is slow to move. Best to avoid the counter if possible.
Getting from one terminal to another is easy. Just exit your arrival terminal and look for the inter-terminal shuttle. Signs are in English and Spanish. The buses run regularly. Just make sure you get on the correct shuttle. If I recall correctly, not all shuttles go to all terminals. Just ask "Terminal cuatro?"
Hope this helps.