Welcome to the addiction.
1. As to starter boxes, the Orks are one of the best. As an Army, there is no better, and easier one to get into on a budget. To both of you, before you get too deep into the game, get the rulebook, and the codex. As of now, the game is in it's revamp, so you are expecting to have a 7th edition codex, and the "New" one. I say hold off, and do the smart thing. Use your same small force, and build on it.
Orks need a boss, a nob on the end of the mobs, and boys, and lots of them. You are going to need to figure out if you like to shooty, or do you like to get them stuck in in hand to hand, because they go in different directions. A good way to get in there is
th get a few squads of the inexpensive single pistol/ hand weapon troops for sale for a song and a dance. THEN add on a couple of the 10 man boyz boxes.
To start with, you can use 2 nobs for the beginnings of squads, and add the boyz as you get more, or you can use the 5 nobs on their own, and mob them up.
That beginner box is a good starter 500 points, if you play it right. The painboy, your mob with a Nob, enough parts to make one of the Nobs a Mek, and the deff dread. You can use one of the Nobws for the Boss for the time being, and add in the other two to give him a meat shield, until you come across a couple more Nobs to add to the force.
You can start out with the 6 Nobs in the box, and fill them in with 5 squads, and add in as you go, a truck each to get the around in. for the Grots, you can build yourself some Artillery out of scrap and some vehicle parts, and little bitz out of the bitz box, as well as the artillery, you can build yourself a few trucks out of scrap, bitz, and plasticard on a budget, or some off the shelf plastic toy trucks that you rip apart.
Orks are pretty resourceful, as well. You can even take some of the Nid scrap and put it to work in your models.
Grotz are ok, they have their uses. Most importantly, (To me) they are great for the artillery pieces. You want to make at leat 3, but you have enough runties for 3 or 5.
THAT is a lot of info. BUT- it is fluid, and it can change, as long as you remember- Orks like to shoot a lot of Dakka, or they like to thump on people with alotta choppa.
It evolves from a basic mob lead by the larger Nob, and you will decide on the weapon loadout for them. Vehicles are ramshacled up out of scrap, and you really do not have to throw that cash at specific
GW trucks. You can also scrap together Killer Kans, Dreads, Trucks, Buggies, bikes out of scrap, other army vehicles, cheap throw away or second and third hand
40K stuff.
To paint-
Clean, prep and prime the model.
get the sprue, wash the sprue, cut off the parts with clippers and the pin knife. glue the models together, prime the model. three color opera the model to get it on the table, and you cn go back between games and continue to paint them until you are satisfied, then protect coat the model.
Check out YouTube for the tips, and ideas, but on the whole, it is all about personal work. Highlights last.
GW paints/ villajo, army painter are the big three, but it goes to personal preference.
go here for the color comparison chart.
https://www.dakkadakka.com/wiki/en/Paint_Range_Compatibility_Chart