diet so pleased for you.
I would try to catch up with him and offer to help. Get as much advice from.him as you can. Ask him where he thinks you should put your seedlings. That way it feels like he is helping you instead of you bumping him off the plot.
If the plot is big enough you could always ask him if he wants to keep a corner of it this year if he has anything still growing and/or find out where he stays and bring him produce in teturn for all the tools etc.
A friend of mine did thiseith her elderly allotment neighbour when she took pn her lit and made a good friend.
I imagine after all that time he might find it hard to give it up entirely.
As for seedlings. If they are wee tiny and in trays, just transfer them to bigger pots several at a time. I.e. i have a 5 inch pot with about 5 beetroot in it because they were only two leaf seedlings. They can stay there a bit longer before going in the ground but they get more depth than in the propagator
Some seeds you can plant into pots and then out, that way they are easier yo see. I have Still got a pot full of leeks to go in. They are now at about chive thickness. If i had put them straight in ground they'd have been swamped by weeds.