Since there are a whole lot of directions you could try to push for improvements in, stop and ask yourself: which parts of your current workflow take the most time or are most cumbersome? What is keeping you from getting more/new business? If your job intake is small enough that a legal pad works, even if it makes you cringe, leave it as it is. People only have so much capacity for change at once - so don't tire them out with things they can't see a need for.
Once you find that "thing", whatever it is, do up some kind of prototype or small-scale version so people can see for themselves how it'd be better. Shine and polish it a bit before you show it because people can get hung up on tiny, fixable details and discard the whole concept not understanding which parts are trivial to change and which ones aren't. Once you relieve the pressure on one part of a workflow, other pain points will become more obvious to people and you'll have some credibility to suggest further changes.
General advice on introducing technology solutions to tech-adverse people: it's all about ease of use. Bookmark that website they need to go to as an alias on their desktop and teach their browser to auto-fill the password. Spend time formatting Excel files to be visually pleasing and easy to read. Ask for feedback about what's hard to do or what they wish they could change and then go make the changes.
And my personal advice about advertising would be to ditch the email marketing idea if you're that small of a shop. If your market is random consumers, you'd be better served by a clean, simple website they can find on Google. If your market is other businesses or offices, you'd be better served by hiring a sales rep to go around visiting your existing clients and trying to win the business of new ones. Just my two cents.