Over the last 3-4 years, I have had at least 7-8 pin holes develop in the 1/2" copper water pipes in the basement of my house (build 1964 so pipes are ~50 y.o.). It has gotten to the point that I need to replace the water pipes in as much as the house as I have reasonable access to. My house has a full, below grade basement, with water service coming in near the basement floor (1/2" copper) through the flow meter, then makes a run of about 25' to the water heater. Just before the water heater is a T that supplies the cold lines to the rest of the house. The cold line in the basement goes to the stationary tub, the kitchen sink (first floor), and to the first floor powder room, and a run to the second floor baths rooms (2). The hot water line follows parallel routing after exiting the hot water tank. All lines are 1/2" copper. Basement is heated/living area.
After doing some reading, I am pretty much decided on redoing the piping with PEX. While I learned to sweat fit copper 40 years ago as an apprentice, I changed fields and have rarely done copper pipe rework, only on emergency repair basis.
I have a few questions for the experts who do this for a living and I seek their advice.
1. Given that the ID of 1/2" PEX is slightly smaller than that of 1/2" copper, should I use 5/8" PEX for all the lines in the basement? I currently don't have any water pressure or low flow issues.

2. I would like pointers to where I can get 'trade quality' PEX components and, more importantly, tools, e.g. crimper and rings. Good brand name mfg suggestions are appreciated - dont' want 3rd world knockoffs..I don't mind paying for good quality tools.

3. I am strongly considering following the existing piping with PEX (using 'T's and elbows as necessary) as opposed to using a manifold. There doesn't seem to be a good location to mount a manifold. Is there any problem with this approach that I should be aware of? I do understand the convenience of shutting off individual lines at the manifold but each fixture has shutoff valves local to the fixture.

Advice is greatly appreciated. Thank you!
-John

You need 3/4" pipe for your main line and 1/2" for the branches.
Avoid Zurn fittings and tools. Viega is good.

a manifold system with individual shut offs helps greatly during the repiping period. you can turn on areas and leave others off. after completion, i agree, there are individual stops under each sink and toilet.
as suggested, use 3/4 for the mains and 1/2 inch for branches.
viega is what i ues but there products are sold at plumbing supply houses not at big box stores.
you also would need 2 press tools. one 3/4 and one 1/2..

We are using viega for almost 10 years now, no issues with them. 20mm / 5/8" for external and 15mm/1/2" for internal would be pretty much Ok. Just a word of caution: whenever we have partially changed from metal pipes to plastic (in this case pex), sometimes lime scale deposits starts clogging your aerators because plastic pipe doesn't allow any scaling to happen. It will happen for while but then would start disappearing.