Alright, first off all, this would have better fitted in the Mission Help forum. Anyway:
1. At the start you've got a bunch of unlocked weapons. The best ones are though, in my opinion, the AK-47, M4, Sawn-Off Shotgun, MP5 (SMG) & Sniper Rifle. I've taken a picture of a map, which shows you all the available weapons, and those huge red arrows show you the most powerful ones.
2. You could go to one of the Well Stacked Pizza Co restaurants. Carl has got a limit in eating. If he eats more than 11 meals, he'll puke and automatically he'll lost everything. If you want to push the limit, and feed him with 11 meals, I think you'd better count them. The fastest way to become fat, is when you go to Well Stacked Pizza Co, press left twice until you'll see a "Full Rack" - probably the biggest available meal. It costs 10$ so 11 of those would be 110$. As I said, Carl will become extremely fat, about a half if he's complete skinny.
3. The side missions are a lot, but considering that you only want the ones that you can do at the very beginning, those would be: Paramedic (Go to Montgomery, it's a little easier), Vigilante (you'll need a bunch of weapons, armor, full health and a ton of luck - doing it by Police Bike & Drive-By), Taxi (boring as hell), Pimping & Firefighter. Those are the cars missions. Then you have the Roboi's Food Mart (here
), the BMX Challenge (you'd better get maxim skill if you wanna have no problems), 100 Tags (SAMA
), available Los Santos Oysters (SAMA
), Los Santos GYM moves, 8-Track event & buying safe houses. This would be everything. Sure, if you wanna risk and challenge yourself to do some 4-star stuff, you can collect all snapshots, horseshoes, so Las Venturas & San Fierro GYM moves, all the other events, NRG Challenge, and whatnot.
4. There are 4 safe houses available for 10,000$ and those are: Willowfield, Verdant Bluffs, Jerfferson & Verona Beach (not the one near the sand).
5. You really can't. It's all up to you. Still, there's a trick I know: save before going to the betting shop, and if you lose, simply load the save file before going to the betting shop, and try again.
6. Everything I listed at number 3, excepting the Vigilante. The cops will automatically try to chase you down, although you indirectly work for them, for blowing vehicles, killing people, etc. It's risky.
7. I really don't understand what you're trying to ask.
8. Well, even if you don't buy any safe houses until you get there, you'll have to go to the closer one. And that's Verdant Meadows. There's no other way to get faster than by car. That, until you'll cheat for a Jet.
9. Side missions will never become harder or easier. There are some missions that helps you to do them easier, yet they're just as hard / easy as always. Some of the would be: Vigilante after passing Flying School (far easier to do Vigilante using the Hunter), Horseshoes after Black Project (using the Jet-Pack), NRG-500 Challenge after Bike School (maxing the Bike Skill).
10. You're welcome.