I'm also pretty new to the game so I've been starting new games when I learn something new, that generally changes the way I want to proceed. I also have a seriously bad habit of starting new games in 4x games when I have a change of heart in how I want to proceed with my strategy. Anyways as far as your questions I might have a few cents to add for a few:
1) No idea, but I don't think labor costs are anything to worry about when you first start out.
2)After many new starts like yourself, I've come to realize that in the beginning building any smaller commercial ships seems pointless, and for myself it seems like when I would make a smaller ship I would just end up needing more. So I would say try to start off with the biggest ships you can get your hands on that can still move fairly fast with your lower tech level. How is see it is this: When starting off with smaller ships, everything else takes longer to do (transporting precious mines to resource rich bodies). When these trivial tasks start taking too long, it significantly reduces your production, and if your starting Earth resources are bad you can run into problems early if it takes you months just to move 40 or 50 mines to say Titan (Titan always seems to have good resources in my games so far).
I guess a lot of this depends on how your using, or if your using, your starting tech points and/or your OB points. I like to build as big as possible for my commercial classes, then use my OB to get a few to start off with. This sets me up just fine until I'm able to produce these monsters (at least what I think as monsters) at my home base.
3) Like Slashmonger says, so much of this game is personal choice that you can really do whatever you want. I like to build asteroid miners, while I've seen most people prefer to just concentrate on automated mines and move them from place to place. And remember, building new classes is free, so there really isn't any reason to not have a class for any and every situation you can think of.
4)Again, it's all just personal choice. For me there are just too many different choices with either to pick just one. Some kinds of pie are awesome, and some kinds of cake are awesome, pick just one and your more than likely going to miss out on something delicious.
Here are some of the classes I started my last game with, and I am loving them so far. For techs I try to start with Improved Cargo Handling, Improved Geo Survey Sensors, and Ion Engines.
Peridot class Geosurvey Ship 1,400 tons 128 Crew 430 BP TCS 28 TH 126 EM 0
4500 km/s Armour 1-11 Shields 0-0 Sensors 1/1/0/4 Damage Control Rating 1 PPV 0
Annual Failure Rate: 15% IFR: 0.2% Maint Capacity 192 MSP Max Repair 150 MSP Est Time: 3.54 Years
Ion Engine E7.7 (2) Power 63 Fuel Use 77% Signature 63 Armour 0 Exp 7%
Fuel Capacity 50,000 Litres Range 83.5 billion km (214 days at full power)
Active Search Sensor MR5-R100 (1) GPS 1000 Range 5.0m km Resolution 100
Improved Geological Sensors (2) 4 Survey Points Per Hour
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Topaz class Gravsurvey Ship 1,400 tons 128 Crew 330 BP TCS 28 TH 126 EM 0
4500 km/s Armour 1-11 Shields 0-0 Sensors 1/1/2/0 Damage Control Rating 1 PPV 0
Annual Failure Rate: 15% IFR: 0.2% Maint Capacity 147 MSP Max Repair 100 MSP Est Time: 3.84 Years
Ion Engine E7.7 (2) Power 63 Fuel Use 77% Signature 63 Armour 0 Exp 7%
Fuel Capacity 50,000 Litres Range 83.5 billion km (214 days at full power)
Active Search Sensor MR5-R100 (1) GPS 1000 Range 5.0m km Resolution 100
Gravitational Survey Sensors (2) 2 Survey Points Per Hour
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Emerald class Freighter 32,750 tons 208 Crew 471 BP TCS 655 TH 788 EM 0
1203 km/s Armour 1-91 Shields 0-0 Sensors 1/1/0/0 Damage Control Rating 1 PPV 0
Maint Capacity 9 MSP Max Repair 40 MSP
Cargo 25000 Cargo Handling Multiplier 30
Ion Engine E0.77 (5) Power 157.5 Fuel Use 7.7% Signature 157.5 Armour 0 Exp 1%
Fuel Capacity 50,000 Litres Range 35.7 billion km (343 days at full power)
Active Search Sensor MR5-R100 (1) GPS 1000 Range 5.0m km Resolution 100
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Ruby class Frigate 62,050 tons 318 Crew 719.5 BP TCS 1241 TH 1260 EM 0
1015 km/s Armour 1-139 Shields 0-0 Sensors 1/1/0/0 Damage Control Rating 1 PPV 0
Maint Capacity 7 MSP Max Repair 40 MSP
Cargo 50000 Cargo Handling Multiplier 40
Ion Engine E0.77 (8) Power 157.5 Fuel Use 7.7% Signature 157.5 Armour 0 Exp 1%
Fuel Capacity 50,000 Litres Range 18.8 billion km (214 days at full power)
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Pickaxe class Asteroid Miner 58,000 tons 1168 Crew 1638.5 BP TCS 1160 TH 788 EM 0
679 km/s Armour 1-133 Shields 0-0 Sensors 1/1/0/0 Damage Control Rating 1 PPV 0
Maint Capacity 18 MSP Max Repair 120 MSP
Asteroid Miner: 10 module(s) producing 160 tons per mineral per annum
Ion Engine E0.77 (5) Power 157.5 Fuel Use 7.7% Signature 157.5 Armour 0 Exp 1%
Fuel Capacity 50,000 Litres Range 20.1 billion km (343 days at full power)
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Garnet class Science Vessel 850 tons 78 Crew 127 BP TCS 17 TH 126 EM 0
7411 km/s Armour 1-7 Shields 0-0 Sensors 1/1/0/0 Damage Control Rating 1 PPV 0
Annual Failure Rate: 5% IFR: 0.1% Maint Capacity 93 MSP Max Repair 32 MSP Est Time: 9.53 Years
Ion Engine E7.7 (2) Power 63 Fuel Use 77% Signature 63 Armour 0 Exp 7%
Fuel Capacity 50,000 Litres Range 137.5 billion km (214 days at full power)
Active Search Sensor MR5-R100 (1) GPS 1000 Range 5.0m km Resolution 100
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Jade class Luxury Liner 13,250 tons 478 Crew 590 BP TCS 265 TH 315 EM 0
1188 km/s Armour 1-49 Shields 0-0 Sensors 1/1/0/0 Damage Control Rating 1 PPV 0
Maint Capacity 28 MSP Max Repair 40 MSP
Passengers 1000
Ion Engine E0.77 (2) Power 157.5 Fuel Use 7.7% Signature 157.5 Armour 0 Exp 1%
Fuel Capacity 50,000 Litres Range 88.2 billion km (858 days at full power)
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Opal class Colony Ship 30,050 tons 218 Crew 1301 BP TCS 601 TH 472 EM 0
785 km/s Armour 1-86 Shields 0-0 Sensors 1/1/0/0 Damage Control Rating 1 PPV 0
Maint Capacity 27 MSP Max Repair 40 MSP
Colonists 100000 Cargo Handling Multiplier 20
Ion Engine E0.77 (3) Power 157.5 Fuel Use 7.7% Signature 157.5 Armour 0 Exp 1%
Fuel Capacity 50,000 Litres Range 38.9 billion km (573 days at full power)