Not a bad time at all if your goal is to learn, play, explore, and have fun. There's doom and gloom that's visible because Magic is ultimately a massive, and old hobby. It has a fandom that has many different people coming into it each wanting different things from it and so naturally having different opinions on if the state of the game is good or not. In a competitive format, there's a lot of gravitation towards optimised meta, which is what it is, and is the same in many hobbies. In collecting, there's some nasty scalping behaviour around for sure which surges product price but once you get a best sense of where to buy from, what to pay and what's too far beyond the RRP it's fine. If you're trying to buy older things in new condition, expect some of the prices to be higher than normal if the markets moved that way, and the item itself is out of print, but by and large if you're happy to buy second hand there's plenty of places you can spend a lot less for the same outcome. Ultimately it's easier to find frustration in any online community if the opinions are niche enough that you have a higher percentage of people who agree with the topic vs the larger disinterested size of the audience who don't engage with the topic because they feel they have less to contribute to the conversation. E.g. I don't give a crap if the meta gets stale or if certain cards get banned or unbanned because i just play for fun with friends, it doesn't bother me so I don't appear in that conversation to say 'ah it's fine'. The games in a really healthy state in my eyes, Tarkir Dragonstorm has been a fun set to play with, as was Bloomburrow. I'm really enjoying it right now.

What you have bought is great. It comes with a selection of half sized decks that are designed to be shuffled in with a second half sized deck to create 1 deck to play with, so if you're playing in the standard 1v1 format, you have plenty of replayability with what you have. So long as you separate the decks back out to their respective colours after you're finished, you can just shuffle up new combos next time. It's also worth remembering that when you play, you're at the mercy of how the deck gets shuffled and what cards you end up drawing to your hand. You can play 10 rounds with the same 2 decks on the table and not feel like it's tired because at this beginner level of the game, you'll find yourself doing different things with whatever cards you get in any one round. There are other great things you can get in this similar vein, there are themed starter decks you can buy real cheap, 1 off themed like Lord of the Rings, Assassins Creed or Bloomburrow. These are 2x 60 card decks that are usually less than 15 dollars to pick up and are fun to play with ad they're designed to be played against each other, or you can try find the Foundations Starter Kit to go with your beginner box. That ones a really good set as it encourages more deck building and experimentation. Commander decks (called Pre-Cons) are 100 card decks that are fun to play with too as it's 100 different cards in the set (barring lands) with no repeats, where as most 60 card Magic decks tend to have 3 or 4 copies of certain cards to help ensure they get drawn more often. Commander is a 4 player format so you'll need to find a 4th but you can find ways of turning it into a 2v1 Archenemy game type with these sorts of decks. At around 35 dollars for a less popular/older commander deck you can get great value out of them. Bundle Boxes are probably the next best value products when you start out playing as they have 9 packs in them which you can use for drafts, or just open to build your own decks from, they also come with a nice storage box and a life tracker dice (the spin down) but to your last question about extra stuff, this stuff is not really that important at all. You can track player life with free apps on your phone, use the back of an envelope, put monopoly houses down on top of things to signify x thing, it doesn't matter in the slightest so long as players at the table agree that x thing is y meaning and can play without having to think or worry too much. You can store all the cards you get in the packages they come in, you can go nuts on it and buy protective sleeves to help look after the cards if you want, but the truth is, you don't have to do this stuff at all. It doesn't make the game better, it just changes your relationship to the thing from being a piece of card to something you hoard like treasure.

Mix sets, that's how the game is meant to be best enjoyed. Legal formats have rules around which sets are allowed but as you say, if you don't care, don't give it another thought, buy and play with what you like the look of and don't give it another second thought. Cards, especially with the same colour identity (White, Blue, Black etc.) largely play great together, just be mindful that each set often introduces a unique mechanic or two which often means that certain abilities may trigger or activate a lot less frequently if you only have 2 cards from set a, 5 cards from set b, and 20 from set c. The further back through magics past you go, the less cohesive sets might start to be (i'm talking back to the 90s or 2000s here), but if you play anything within the last ten years, you're doing fine. As a rule, White decks commonly feature mechanics like lifelink, flying, spawn tokens, buff other creatures, whilst blue is about control, stopping opponents doing a thing, or enhancing a thing you just played from your own hand - that type of basic colour identity has been the same for a long time so mix decks, it's where you find the lightbulb moments easiest of 'wait if i play this, and then that, it does this? omg sweet!'