I haven’t run the low level missions in a fairly long time so I can’t give realistic estimates but I can give some guidelines. I roughly remember the mission rewards increasing by 5 to 10 times for each level.
Lv1s pay out rather poorly, but I think it’s largely okay as you are just trying to get a frigate/destroyer setup, and save up some isk and train some skills where you will pretty quickly move on. Heck if you do the tutorials and run the SoE epic arc you can probably just skip level ones and go right to level 2s.
lv2. a bit more isk, and a bit more challenge than lv1s, if you have anything approaching a well fit ship you should quickly learn to faceroll these missions. I did a handful of these to grind standings a while back, pretty much just warped in and shot everything till the mission check mark popped up.
lv3s things start to get interesting. You can get something like 1000 LP for each mission and some have a bunch of NPCs for some nice bounties. Take the time to learn the trigger system and the blitzes for the missions. With skills most missions take about 5-6 mins each. I’d suggest sticking to these for a bit to make some isk, there’s a certain skill level where you make more blitzing 3s than struggling through lv4s.
lv4s, here’s where you can get some of the best isk in highsec (heck beats a lot of what I’ve heard from other areas), there’s a bit of a learning curve but if you mastered blitzing lv3s you should pretty quickly learn the lv4s. Just might need to take some time to grind up the standings, and train up the skills to really succeed. I was doing these about 4-5 months into the game, and that was back when learning skills were still a thing so that slowed me down some, plus I did some extra standings grinding as you needed standings for jump clones. A focused 3 month character can start there, but i don’t know that it’s efficient. At some point it’s worth it to make the jump and start to learn the triggers and start to blitz where you can. And start training into burner ships. A roughly year old pilot should be able to do blitzing at a high level, and if you get really into it you can pick up some injectors to speed things up.
This thread has a lot on blitzing lv4s, that said it’s starting to get outdated with each patch, but most of the core info is right, The mission list and a few fits might not be right. Blitz and Burner Guide v1.2.3
For the burner missions it’s also worth checking this thread, My post is up to date afaik with a bunch of cap stable setups. And when things get changed in a patch there’s usually a post there pretty quickly Burner Mission - Ship advice to solo them including fittings
lv5s. lowsec only missions, often blitzed with multiple alts to pull missions. I don’t have any good data on these.