If you're really into Altcoins then you should definitely give enough time to research and testing because many times top 10 altcoins also got devalued without any warning. I would encourage you to study the case of Terra Luna because once that coin was also among the top 10 cryptocurrencies but in a week it lost most of its value and many investors have lost a lot of their investment due to Luna crash.
Absolutely, I agree with you regarding Terra Luna being one of the toughest lessons for crypto investors in 2022. However, let's not forget how massively Luna grew when Bitcoin broke its previous peak, right? So, if you don't get too greedy, imagine the profits you can make with Altcoins, including Luna.
If you still want to go with the altcoins then I recommend you to stick with the ones that have been doing great for many years. Some people may recommend you to go with Arbitrum or Polygon (MATIC) but I think those are still new in market and both of them can suffer huge value drops. I'm sure that if you diversify your $30k on ETH, BNB, LTC, Doge, and to some extent XRP, then you'll still be safe from losing your capital. The XRP may not get much higher in value but it's the safest among all of those because it will continue to survive in next bull run.
Thank you for your suggestion, Arbitrum is also one of the good coins in my portfolio for the upcoming bull run cycle. I have strong confidence in the L2 trend taking off, and Arbitrum is one of the platforms that shouldn't be overlooked.