Long time 2boxer New to 5boxer

[Zub]

1. The group configuration. I know its hard. I know and read that the best beginner's combination is a Paladin x 4shamans, or 5shamans or 5 druid combination. Something that doesn't require a huge pile of macros on each character and configuration on the IS boxer. So should I first make the 1xpala (which I got already) and 4x Shaman at start, then slowly start with other combination to get the hang of 5boxing? (Note: i don't have RAF. Its my 4 account and last account I got it from a friend who no longer plays and deleted all of his chars. I just moved my shaman on account 1 to that account).

It's not hard, it just takes longer to configure.
The important thing is to have an idea of how the classes work. Then you can pick the 3/4/5/n abilities to use and start making macros. Start with simple ones (like those you listed) and add to them as you go.
If I were you, i'd jump directly into the mixed team. Just because at least you'll be advancing while trying things out and won't have the feeling of wasted time.
I personal use about 9 main macros for my toons, so that's 9 keys for 90% of the play actions
- 1/ buff. Each toon has a macro that casts all possible buffs on the party. i use it at the start of an instance or after a wipe
- 2/ prep. pre-pull action (PoM, Totems, switch to correct form etc)
- 3/ pull sequence. the tank starts building agro alone
- 4/ dps rotation. each toon starts dpsing, the tank has his tanking rotation, and the healer has a tank healing rotation
- 5/ special. each toon has his special abilities (starfall, bloodlust, treants)
- 6/ aoe: Fire Nova, Hurricane, Blizzard, holy nova etc
- 7/ help: each toon has his oh shit botton (ice block, desperate prayer etc)
- 8/ regen: shadowfiend, managem, innervate etc
- 9/ taunt: tank taunt, dps and heals throw threat reducers (wind shear, fade etc)

a normal pull just goes like this: 2-3-4-4-4-4-4-4-4-4-loot . The other keys are just 'in case'
added to that you have utility macros (hearth, eat/drink, accept LFD etc)

having a group with 4 of the same class will not make it simpler in terms of how things work, it's just the name of the abilities in the macros that will be different.

2. The healing. This is the part I need to read more of the guide. But I heard healbot+something about mouse repeater should do the trick. But I also heard about making clickbuttons from the ISboxer and macro it on the healer. Would like to know which is easier since opinions varied on most posts.

i currently use a castsequence with alot of empty comas, and put it on the same keybind as my dps.
if things go bad i press it quicker :-)
That macro also has a circle of healing cast on cooldown. Starting to look into mouse passing, but using keyclone atm so trying to work it out a bit without atm.

3. Keyboard. Should I get a G11/G15 keyboard to make my life easier? Or should the standard keyboard would be enough? I kind of expect the answer but would like to make up my mind on purchasign an expensive piece of hardware or not.

i use the num keypad on my normal keyboard for my macros. I've only got a limited number so it all fits in a nice, square layout.
and i use F8-F12 for my pip switching.

Take all that with a grain of salt, i havent been 5-boxing long. been around a bit however.