Been there...... done that...... you WILL be fine!
Last March I was diagnosed with a Stage II Grade 3 tumor (3.4cm??) in my right breast that they thought was just a cyst as well. And I was 35 with no history of breast cancer in either side of my family! Just my lucky day I guess ;-).
Had the offending boob ripped out within 9 days, and started chemo about four weeks after that. Given that it was a grade 3 tumor they recommended what I call "chemo-max" as opposed to the "chemo-lite" if it was a lesser grade. It was an interesting time for sure..... I did 6 treatments 3 weeks apart, the first 3 were chemos with the initials "FEC" - sorry, don't have the exact details of which ones they were, and the first few days after were fine, then uncomfortable for about 5 days (flu-like, nausea, general tiredness), and then probably about 90% 'normal' for the next two weeks. Honestly, I felt a bit guilty being off work ;-). Didn't throw up once, and actually GAINED weight through the whole process. Darn steroids. Started to lose my hair after the first treatment, so had it all shaved off before the second. Was kindof a cool feeling to get 'clipped' ;-).
Second set of 3 treatments were a bit harder. It was the "D" chemo, docetaxel or something like that?? Still same pattern, fine for a few days, then quite uncomfortable for about 5 days, then ok for the next two weeks. By the 5th and 6th treatments though, my stamina was shot. Couldn't make it up a set of stairs without pausing, couldn't bend my joints, and had lovely fluid buildup all through my body. Felt like a water filled balloon! My last chemo was in August, and I could feel, week to week how much better everything was starting to feel. It's now, what, February, and I honestly feel 95% back to where I was, with only lingering joint pain (and an extra 20 pounds) still around.
It's great that you are able to get the reconstruction at the same time. Mine is scheduled for the end of February, and I'm getting them to take the other boob out as well (they found lumps in it just after Christmas, and even if they are benign this time, I'm not sitting around with a ticking time bomb in my chest!). Not looking forward to that, but if it's anything like the last time, then it's definitely tolerable. It hurt of course, but wasn't nearly as debilitating as I thought it would be. Us horse folks are tougher than the average I think!
Now of course, the most important aspect. Horses!! I had to take a month off after the surgery to let the area heal, and for about a month after that I didn't have the upper body strength to tack my horse up myself (raising arms above rib height was hard....) or even putting a halter on, but luckily had friends and the barn workers that would help me with that. My mare was luckily very easy going about it all, since for the most part we just walked around.
I was able to ride all through chemo, but obviously didn't during what I called "the week of hell" each time, since I barely left my couch :-/. My oncologist just begged me not to jump, as she was scared of what a fall could do to my already pathetic immune system, which I easily complied with. I was just happy to be able to get on. Again that whole lack of stamina thing didn't exactly make me want to do more than walk around, but better than nothing.
As for working around the horses, weeks 2 and 3 I was able to do most things myself, but wouldn't have been able to have the strength/stamina if one of the horses decided to do something naughty either on the ground or in the saddle. Luckily I'm surrounded by good people that would help me out, but I would strongly suggest that you make sure that you have others around to help pull a stuck foal out or catch a feisty mare as you might not have it in you.
As others have said, chemo and surgery affects everyone differently, and as weird as it sounds, I hope you have it as easy or easier than I did. Drugs are your friend and definitely ask for the good stuff. My oncologist's goal was to make sure I didn't throw up once, and although there were a few close calls, I was stubborn enough to want to meet her expectations :-). She swore by a drug called Zofran and that plus the Dex really kept my nausea in check. Also something called Maxeran to keep the guts moving since everything wants to just shut down....
Anyhow..... just relaying my story in the hopes that it helps. I'm coming up to my one year anniversary of finding my lump (Feb 18th) and it's been an interesting ride.
Chin up, you're tough, your mares need you, and you WILL be fine! PM me if you ever need anything!