I can't speak too much to adopting outside your chosen age range, but we did the same age ranges and siblings. It's been great, but also exhausting. Loads of stuff that I would have said is covered above, but just few random bits below from our experience for you to ponder on:
Your friends are right, you do get them at a good stage. A chunk of time off work to bond with them before obligatory school means you can get the sweet spot of doing cool stuff with them whilst they also kind of remember it. We do loads of stuff with ours that we couldn't if they were a bit older or a bit younger. That being said, we do it alone because all our friends are back at work. It is an unusual position to be saying you are on maternity when they are older, and it obviously comes up a lot when you attend stay and plays or groups or whatever. Either that or your kids are the oldest at events. Which leads me to the next thing...
Having adventurous and bold kids is bloody hard work. We have two of them, and by God it is knackering. Climbing, running, jumping on the sofa, throwing stuff to see how high they can get it, licking snails to see how they taste, etc. It can be a sign of sensory processing disorder (in the process of being asssessed), which can be tricky to manage because it is a need that seems to never be truly met in ours. What that means in practicality is that they NEED exercise come rain or shine, and long long walks, more so than other kids. They also barrel into places with zero fear and 100% noise and energy, which can be hard socially because you feel like you are continually gasping and saying PLEASE STOP CLIMBING ON THE CLIFF NO NO THATS NOT FOR JUMPI- NOT THE ROCKS AGAIN FOR THE LOVE OF.... etc. Thats hard because you are often the onlynone saying it. With adoption it also comes with something we didn't consider, which is that every time ours get injured doing whatever they were doing, we have to have a social worker visit. The FC had them in buggies all the time partly we think because they were worried about their behaviour, and the riskiness of it. One fell face first onto a rock whilst carrying a log he didnt want to put down, bruising his face, the other rolled down a hill too hard, etc. We self report anything significant to the MASH team as we are pre AO, and so the kids social worker knows us and the kids, but it is a stress because at under a certain age they can't self report so they have to be seen in person, which means an on the day visit from a SW to verify the kids are OK, which means changing all your plans. At 2 and 3 they are also mobile enough to be practicing their independence but also clumsy enough to need your support, which can be hard if you are still bonding with them. Adventurous kids are never dull, but it can be hard especially if you let them take risks. It's a much finer balancing act than I thought it would be! My 3 nearly 4 year old climbs things designed for 10 and 12 year old, but still sometimes runs like a toddler and thinks like a toddler.
The age range is also something people want to talk about a lot. It comes up all the time, in the supermarket, at school gates, on the street. If I had a pound for an unhelpful "ooh, you've got your hands full! 2 under 2 were they?" Comment I wouldn't have to end my adoption leave.
Going from 2 to 4 is huge. There are so many more dynamics to consider, their sibling one as well. Ours tag team with each other to outsiders, so if one gets in an argument the other barrels in too, yet they tell tales like nobody's business if it suits them. You have an immediate family, but also need to think that if you are the stay at home parent you will be the one dealing with the two of them, and then they outnumber you. What happens when you need to leave the park and one refuses? For example, when I go out of our local area I take a buggy so that I can keep one in one place and chase the other wherever they are going. In our local area I have a continual supply of chocolate waffles that I threaten to eat if they don't come and that works. A 2 year can put on a surprising burst of speed when they want to! It's the same at doctors appointments- you have to take both, but by God it is tricky to manage, and some of the appointments can be long and require delicate conversations as you get to know the services involved or transfer them to your providers. It's hard with two toddlers who will only watch one episode max of Chuggington on a phone before deciding that the scalpel tray and sharps box is way more interesting just as the GP is telling you about how much medication to give and why.
Other things to consider are nursery options. Ours will be in the same class for a term, so that's worth thinking about.
Their neurodevelopmental needs may not be obvious, so we have spent a lot of time at medical appointments trying to work out whether they can't hear us or are ignoring us, whether the waking up at night is coughing or nightmares or trauma etc.
We also found that becoming parents to toddlers required a very steep learning curve about developmental milestones and what is and isn't normal, health visitors, red books, all that stuff, but usually with two very noisy toddlers in tow. Also getting people to take stuff seriously is hard because they are young, but we keep reiterating the importance of early intervention.
We had to get two bins because both of ours were still in nappies, which was a whole load more admin from the council.
Regression meant our youngest language was delayed, which wasn't necessarily a problem intellectually but meant he couldn't communicate his needs with us beyond crying and screaming, but he needed much more nuance than that. Add to that we were (are!) Inexperienced parents who had a child we really didn't know much about and those first months were incredibly hard. He can now, but we hadn't factored in how much this would impact his emotional wellbeing.
We changed so many nappies, rocked to sleep so many times and fed so many bottles that we didn't feel we had missed out too much on the baby stage.
However, there are loads of benefits. Hand-me-downs make way more sense for two close in age, they are absolutely hilarious together, they eat the same food, they love the same TV. We have snail pets everywhere, sing songs all the time, we have had the opportunity to make some great memories. It's been the most ridiculous and busy time of our lives, but it hasn't been a traditional maternity leave, so if that is important to you I would think about that.
It is honestly a wonderful time, and I wouldn't change our two for the world. Watching them bond is great, they are just developing their own quirky sense of humour, they can speak so can start to explain what is going on in their little minds, respond to us when we speak.
Hope these things add to your ponderings as things to consider!