[RPG] How is XP awarded for combat encounters

4e is modeled on approximately 10 encounters/level. So if you are playing 2 encounters/session then you will level approximately once every 2.5 months.

The experience point numbers in the game are built so that characters complete eight to ten encounters for every level they gain. In practice, that’s six to eight encounters, one major quest, and one minor quest per character in the party. (DMG 121)

That means that yes it will take you a bit over 2 years to get to L10 playing twice a month and probably longer to reach higher levels as paragon and epic encounters may take longer (higher XP budgets, PC damage doesn't scale as well with monster health at epic etc)

This has been borne out in my experience. My group meets weekly for about 4 hours. We usually get through two combat encounters in a session (or 1 combat and a social encounter or similar). We have been playing for a bit over a year and are nearly at L10.

Theoretically if this math continues (I don't think it scales quite the same way) and you can continue to finish 2 encounters in a session it will take aproximately 150 sessions to get to L30. at 26 sessions/year it will take a bit over 5 and a half years to level all the way to epic.

Addendum:

Here is a breakdown of time taken to Level from 1-30 assuming 2 encounter/session 26 sessions/year at 6, 8, and 10 encounter/level:

• 10 encounter/level -> 300 encounters -> 150 sessions -> 5.76 years
• 8 encounters/level -> 240 encounters -> 120 sessions -> 4.61 years
• 6 encounters/level -> 180 encounter -> 90 sessions -> 3.46 years

This gives you an idea at least of potential different rates at which you can level depending on how challenging your adventuring becomes.

This depends on a number of things. Do your players like to favor combat over other forms of role-playing? How long are your sessions? Do your players understand the rules well enough to where things are going to move by quickly (sounds like no, in this case)? Do you as a DM mind running a lot/a little/no combat in any given session? This sort of thing is highly customizable depending on your needs, and is thus unfortunately somewhat unanswerable.

Anyways, my personal recommendation would be to run a quick module or two before your main campaign. This will allow you to understand the sort of preparation a DM typically has for an encounter, as well as learning a couple of tricks here and there with DMing before you start your own campaign, which, in the long run, will be for the good of your story!

More importantly, it allows you to assess your player's desire for and prowess in combat. If it turns out they only make it through one encounter, then want to roleplay or ask questions or drink beer and relax for the rest of the session, you haven't wasted hours of preparation. But if they turn out to be some kind of death dealing blood-for-the-blood-god-skulls-for-the-skull-throne party, you are unlikely to run out of encounters! You don't even have to finish the module, really. Once you are confident in your ability to prepare adequately for your players, you're all good to go. Happy DMing!