I don't have alloys. I prefer to run steellies because they are cheaper (to replace if I need to) and easier to repair when I'm in the bush. Carry a generator and a small stick welder and you're all set. Carrying TIG for alloys is just too much hassle. Having said that, in the past 40 odd years I've never actually needed to repair a rim when in the bush. On the road I've cracked a few alloys and only ever bent one steel rim. Most tire dealers have rims for sale, choose what you want from there or look on the internet, my current steel rims were around $25 each on ebay.
By the time they rust beyond being usable I'll be pushing up daisies. I also have some 60 series chromies (steelies) in my shed that go well on the hilux. Mixing around Toyota to toyota isn't too hard. Mixing around the manufacturers is where you need to be careful.
Offset (if I'm not mistaken) is where the studsgo through the rim in relation to where the inside side wall of the tyre sits. The wrong amount of offset and your tyres will rub on various parts of your vehicle. Sometimes the guard or sometimes the linkages. You also need to be careful with diameter. 15" rims fit fine on my 2004 hilux, but I was looking at a similar aged Jeep a whole ago and it will not take anything less than a 17" because of the diameter of the brake disc and calipers.
I'm no moderator, but I am guessing that they would prefer you post all your queries (on the same subject) in the same thread, it helps them keep track of things easier.