1. Yep totally, no professional skills are necessary.
2. As Glampetals said 35 and 120 are two different sizes of film. 120 film is bigger so you get photographs with wonderful detail. The Holga takes 120 but it can be converted to 35mm. Pinhole is a whole different kettle of fish and I'm not very clued up on it.
3. This will vary depending where you go, you'll have to find a place that does develop 120 film first, ask around. It's maybe a couple of pounds more than 35mm, so not mind blowingly expensive.
Envoking the knowledge aquired from resident
KR photography expert bigmuff, if you want a medium format camera you might want to look at Lubitels or Seagulls on ebay. They can be bought for around the same price as your Holga but are a better quality camera all round.
However, if you're using it on holiday you might be better off with the hand held Holga, as the Lubitel/Seagull are tricky twin lens waist level viewfinder bastards.
You might already have a 35mm SLR but if not I'd really reccomend buying one off ebay, you can get one for around £20-30 that will give you great quality photos, different from the Holga, and frankly you will look really cool with it

I can highly reccomend the Olympus OM series.
Again, if you're not sure about setting apertures and stuff the Holga might be a better option for now.