More stupid newbie questions I ponder at 3 am when I can’t sleep
If I decide to buy a digital Ham (gmrs isn’t digital I believe) such as say a Yaesu FT70d or 5DR
Can they only use digital repeaters and other digital radios or can they toggle between digital and analog mode and connect to other digital or analog radios and repeaters as needed? 
No such thing as stupid question. Newbie question, yes. LOL.
In answer to your question, digital radios are both analog and digital.
Yaesu uses their own unique digital format called C4FM. Many other ham radios use the far more common DMR. C4FM is an amateur mode proprietary to Yaesu, while DMR is a widely used amateur and business format. It would depend more on your local ham community, what they are using and who you want to talk to.
C4FM is easy to program. DMR takes a lot of work, research and trial and error. C4FM radios are high quality and expensive. DMR radios come in a wide range of quality and price-point models. DMR is far more popular with amateur radio operators. Pick one.
DMR was originally designed as an expert mode, to have experts program them for end users. One issue is that many people don’t want to invest in the time to learn how to program them, and they get frustrated and end up returning their cheap Chinese radio. You get what you pay for.
If you decide to go to DMR, you will have access to a lot more users worldwide, and help is available from users and forums. You will have lots of questions because DMR takes work. Use internet forums to help you decide on the radio. If there are long long threads devoted to helping to solve problems because people bought the cheapest one they could find, avoid that make and model. Check user reviews, and read them carefully. Ignore any reviews that are written by stupid people. (“Couldn’t figure out programming, so returned it.” “Wanted a radio to monitor local police and it doesn’t.” “Couldn’t figure out how to turn it on.” Etc.)
You actually do get what you pay for in many ways with radios. EVERY two-way radio is a compromise of some sort. There is no free lunch; life is not a Hollywood movie and Bill Gates does not want to give you some of his money.
Thanks. If I go digital I’ll definitely need to go the Yaesu route 
Chickenhawk spells it out well. They snag with the radios is that out of the box, they don’t do anything and all the clever stuff is NOT in the manuals, they just tell you what each programming section is called. YOU have to put in the radios what you want, and if you make one teeny error, they don’t work - often don’t work at all!
FM needs one or two frequencies, and possible CTCSS tones and they’re done. They work. DMR is a totally different world, and every radio model is different. Often similar, but always different. The software is often a common looking platform, but between two models there are changes to boxes - different names and purposes, different orders and other menu items that interlink. You may have to put the same data in multiple locations and enter contact lists, scan lists and even import data files or things work weirdly or not at all. It’s no use getting a friend who knows to program them, because somebody will say have you got TG XXX and of course you’ve never heard of it and it’s not in your radio, but the new version of the repeater needs it. DMR is a hobby of itself - Ham radio has a steep learning curve for some people. Digital has this a hundred times harder. The studying people do for their ham licence doesn’t cover any of the digital stuff you need to know, and pretty much people learn it individually. It’s tough.
Yes. What these guys said. An analogy is that the Yaesu C4FM would be like an Apple iPhone, and DMR would be the Android of the digital amateur radio.
Then there is also Icom’s D-Star…
I think I would go with a DMR, myself.