Buying your FIRST Lexus is very scary ..... I remember! Your heart is in your mouth wondering what will go wrong with an older car. Yes, we can all buy a lemon, even a Lexus but overall they are more reliable than people realise. If they do go wrong, it is usually one thing. Yes, that can be expensive and there are some known issues on some models that remedial action can be taken to prevent catastrophic failure. Once an issue is sorted you rarely get others occurring straight away.
If you want a premium brand then you must expect to pay premium prices for parts but a Lexus car is one that you can run successfully at modest cost. I would NEVER (have owned some) again buy an older BMW, VW, Volvo or consider a Merc. I am now on my fourth Lexus - I still have THREE on the drive - and yes we all get a bit twitchy with older cars. My advice would be to buy something that will not break the bank. If it turns out to be a lemon then you can get rid of it and not lose too much money.
Unless you are very unlucky (and some members on here have been BUT still buy another one!) you will be bitten by the quality and engineering. You can always be safe and buy an older Avensis / Camry with a low mileage. Hybrids ARE scary, as the technology is amazing but also complicated. I have an RX 400h and an RX 300. The 300 is a straight V6 and is less likely to go wrong but fuel consumption is heavy compared with my 400h hybrid. You have your Merc baby and want something that stands out as well. A Lexus would be what I would go for and the GS 450h looks a cracking car. Dip your toe in, don't spend too much and have LOW expectations of your purchase ........... I hope you will be pleasantly surprised.
Good luck.