Does Fallout 2 have any time limits like Fallout 1 had?
Fallout 2's only time limit corresponds with the overall time it takes you to complete it, and for that you get 13 years of game time. It's actually enough time for you to cover every grid on the entire map by foot several times over.
How do I give my NPC's weapons and armor and control their behaviors?
You can give them anything you own, but they'll eventually reach their own carry capacity. NPC's in Fallout 2 actually wear armor unlike in Fallout 1... well, only certain armor-capable NPC's will, so giving them a good extra set and telling them to equip it is a good thing. You should also load them up like a mule when possible due to your own carry limit. Unlike in Fallout 1, there is now a handy "Trade" button during your dialogue with them so that you no longer have to use the Steal skill, and it allows free trade between the both of you. Another very handy "Combat Control" button has also been added, which gives you the ability to micromanage their behaviors and equip their best weapon and armor. If you want them to give up the current weapon they are using, just ask them to put away their weapon and then you can trade it from them.
What are some good combat tactics?
Against other melee attackers, especially at the beginning, attack only once and use your remaining action points to run away. The critter will follow and hopefully will not have enough action points of its own to attack. When it's your turn again, attack and run, and repeat until the enemy is dead. Works well on animals especially... like rats, scorpions, etc., and when you have a higher agility.
Another good one is to begin making targeted shots once your skill is decent, and aim for the eyes (or ganglia or sensors... or whatever the enemy has in its "eye" spot). What's a decent skill? If you're attacking from a range, then 90% or higher is about when you can make some decent targeted shots depending on distance. If they're within melee range, you can make targeted shots slightly sooner with some degree of accuracy. Targeted shots increase the chance of a critical hit, which always do more damage.
Against fallen enemies, you can use targeted shots with an increased chance to hit. Try shooting male characters in the groin so they fall down, or anyone in the legs. Then use a targeted shot in the eye to finish them off after they've fallen.
With all of the different types of ammo, how do I decide which to use?
In general, the weapon you decide to use makes that choice for you. Look at its description in your inventory. In some cases, you'll acquire both JHP (jacketed hollow-points) or AP (armor piercing) of the same ammunition type, like with the 10mm JHP, or 10mm AP. The armor piercing (AP) ammo in this game does not work as intended, so I'd advise sticking with the JHP in those cases where you can use both and simply sell off the AP or use it for emergencies.
Is there enough ammo to go around?
In the very beginning, conserve just slightly. Later, you'll have more than you know what to do with, of almost any type. There are a few exceptions, like the rare 9mm Ball... or BB's. Since the weapons that use this type of ammo are generally more like novelty items, you shouldn't be worried about a lack of ammo in this game. Fortunately, many of the enemies you kill will have enough to keep you filled.
What's the maximum level and where will I likely be when I finish?
You can level up to 99 in Fallout 2, unlike the level 21 limit of Fallout 1, and you'll likely be anywhere from 20 to 25 when you finish, if you complete most of the quests. You can always look for random encounters, some of which give a substantial amount each time, and level up even further.
Where is the best place to level up?
Spoilers! I can't imagine that you want to be spoiled being that this is a complete walkthrough.... but I thought I'd warn you just in case. When you're capable enough to defeat them (likely around level 16-20+), travel the wastes between San Francisco and New Reno, and you'll find plenty of the toughest random encounters.