Hi! I personally think it is totally reasonable to take Bio 172, Bio 173, and Chem 125 with the lab in the second semester of freshman year as long as those are the only STEM classes you are taking. You do have to expect a semester with a relatively heavy workload since all of those classes have exams (even lab for 173). However, if you do think that you have other obligations that you need to fulfill next semester, I would say that taking chemistry in the spring/summer is also a great choice. I hope this is somewhat helpful to you and feel free to drop by during our advising hours if you want to chat more! 
PMH Haitong

Hi there! Thank you for your question!
With respect to intro bio, I did the exact same thing you are thinking of doing: 171 first semester, then 172 and 173 second semester. Personally, I thought the workload for 172 was doable, but I will say the exams are fairly different from Bio 171, and it may take some getting used to. 
As for taking Bio along with Chemistry, I personally know several people who have done this and done well. But it really depends on how comfortable you are with Chemistry already- for me, Chemistry has always been a challenge, so I took Chem 130 (or an equivalent of it at a different school) over the summer by itself and did well. But 130 is meant to be an introduction, as are the intro chemistry labs. They are not meant to be devastatingly hard. You can always try out Bio and Chem together for a week or so, in the beginning of next semester, before deciding for sure if the workload is doable.  
I like the idea of taking a psych or social science class along with these two natural sciences. If you have room in your schedule, you could even take a cool humanities class for a nice balance of subjects! But of course, it’s up to you and how comfortable you are.
I hope I answered your question decently! Please let us know if you have any more questions about this!
-Arjun, PMH Advisor