Hello im new to this site and portable modding.
i found my old n64 and my sega dreamcast and i got really interested in doing a portable mod.
i was wondering which of these i should try first. Mainly by how tough it is to do, but also is one system more sensitive than the other. would it be harder to destroy a dc or a 64 in the making of the project because i dont want to buy another console. i dont have skill with electronical modding but i catch on to things fast. i have access to all the tools i would need and i can probably order and parts i need.
so which should i do?
also any advice?

They are both very difficult to do an I don't recommend either one as a starter mod. That being said the Dreamcast would be harder with 3 different voltages and harder triggers and a bigger board. As seen by the lack of DC portables out there it is more difficult.
My advice. Start with a a Snes or Nes portable.

well i dont want to do nes or snes cause theres only 2 or 3 games i like for those systems and i wouldnt want to put work money and time into something i dont want. iv looked over portable n64 topics ALOT and i feel like i could do it with help from the community on here i just want to know what are the odds of me frying one if i was careful and closely followed a guide. is it just like one wrong move BOOM its done or is it like dont do this or it will mess up

My first project was a N64. Do NOT try a portable N64 for your first project. It is a lot harder than most systems out there. It is very easy to fry, very finicky, requires an extremely stable voltage source for 1 of the 2 different power lines, and needs a cooling system. If you accidentally bridge the 2 power lines it's DEAD. The Dreamcast is even more complicated because of the moving parts inside of it. Both are very costly projects to a complete beginner because the odds of your frying both of them are great. Do what hailrazer said - start out with an NES or SNES portable.