pros and cons of the distributions system types for new mod-con install

Hi gang,

I am planning to replace the electric baseboard heating system in my house this year with a NGas mod-con boiler setup.

What are the different system types and their pros and cons as far as plumbing from the boiler to the heat emitters goes (i.e. serially fed, tee-tapped mains, home run, etc.) ?

I will be installing 7 new cast iron rads throughout our small(ish), ~1400 sq. ft. house to provide the required ~35k BTUs determined to keep things warm and toasty inside our abode on the coldest day of the year.

My PEX runs from the boiler / manifold to the rads. should be:
(main flr) Bedroom 1: 27' x 2 (supply-return) (~3200 BTU rad.)
(main flr) Bedroom 2: 21' x2 (~3k BTU rad.)
(main flr) Dining area: 36' x 2 (~5.6k rad.)
(main flr) Living space: 28' x 2 (~5.6k BTU rad.)
(main flr) Sunroom: 30' x 2 (~5.6k BTU rad.)
(lower flr) Living space: 32' x 2 (~5.6k BTU rad.)
(lower flr) Laundry room: 21' x 2 (~5.6k BTU rad.)

Additionally, since I will run all the PEX myself, do you think PEX-Al is worth the extra $$$ vs potential added frustration running regular PEX solo?

Thanks in advance for suggestions, advice and shared experience.